Wiegand using single 485 transceiver

Abstract

A device (102) includes a transceiver circuit (210) and processing circuitry (212). The processing circuitry (212) is configured to disable (DE) a differential drive output (A, B)of the transceiver circuit (210), determine a data transmit time of a Wiegand protocol, apply a data signal to be transmitted to a data input terminal (D) of the transceiver circuit (210) when the differential drive output (DE) is disabled, enable the differential drive output (DE) during the data transmit time, and disable the differential drive output (DE) of the transceiver circuit (210) after the data transmit time.

Description

WIEGAND USING SINGLE 485 TRANSCEIVERTECHNICAL FIELD

[0001] Embodiments illustrated and described herein generally relate to device communication, and in particular to systems and methods for communicating data between devices using a two-line interface.BACKGROUND

[0002] Access control systems grant physical access to an authorized user through a controlled portal such as a secured door. The user proves they have approval to enter by swiping a card using a card reader, entering a person identification number (PIN) or password, etc. A Physical Access Control (PAC) system authenticates and authorizes a person to gain access to a secured area or other resource.

[0003] PAC systems may incorporate a variety of components and utilize one or more different protocols, such as Wiegand, open supervised device protocol (OSDP), universal asynchronous receiver / transmitter (UART), etc. Wiegand communications typically involve analog, one-way signal transmissions over a pair of wires without encryption. OSDP typically provides bidirectional digital data communications with one wire transmitting and the other wire receiving encrypted data. Some systems may include a mix of legacy and modern equipment or a mix of components of varying complexity. For example, a system owner may be in the process of upgrading equipment, or based on the design of the system, certain equipment may deploy high-security features while other equipment may only require medium-level or lower-level security features.

[0004] In order to improve the ease of designing and deploying PAC systems, it is generally desirable to provide increased flexibility and compatibility between PAC system components. However, increased flexibility and compatibility often requires increased chip counts to support the various configurations and combinations of equipment. Improvements to PAC systems are described herein that reduce the cost of a PAC system while still providing improved flexibility and compatibility.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is an illustration of a basic Physical Access Control System (PACS) structure.

[0006] FIG. 2 is a block diagram of portions of an example of an access control system.

[0007] FIGS. 3 A and 3B are illustrations of examples of waveforms of a transceiver circuit to transmit data.

[0008] FIG. 4 is an illustration of another example of waveforms of a transceiver circuit to transmit data.

[0009] FIG. 5 is a flow diagram of an example of a method of operating a reader device.

[0010] FIG. 6 is a block diagram schematic of portions of an example of a reader device of an access control system.DETAILED DESCRIPTION

[0011] FIG. 1 is an illustration of a basic PACS structure useful for an office application. The Access Credential is proof that the holder is allowed to enter a controlled area. The Access Credential may be a data object, a piece of knowledge (e.g., PIN, password, etc.), or a facet of the person’s physical being (e.g., face, fingerprint, etc.) that provides proof of the person’s identity. The Credential Device 104 stores the Access Credential when the Access Credential is a data object. Examples of a Credential Device 104 include a smartcard or smartphone. Other examples of Credential Devices include, but are not limited to, proximity radio frequency identification based (RFID-based) cards, access control cards, credit cards, debit cards, passports, identification cards, key fobs, near field communication (NFC) enabled devices, mobile phones, personal digital assistants (PDAs), tags, or any other device configurable to emulate a virtual credential.

[0012] The Reader device 102 retrieves the Access Credential from the Credential Device 104 when a Credential Device 104 is used. The Reader device 102 may receive the credential information from a card reader. The card reader extracts the credential information when the user swipes the card or taps or inserts a smart card. The Reader device 102 may receive the credential information using wireless communication with a person device of the user such as a smartphone for example. The Reader device 102 sends the Access Credential to the Access Controller 106.

[0013] The Access Controller 106 compares the Access Credential to an Access Control list and grants or denies access based on the comparison, such as by controlling an automatic lock 108 on a door for example. The functionality of an Access Controller 106 maybe included in the Reader device 102. These Reader devices can be referred to as offline readers or standalone readers. If the unlocking mechanism is included as well, a device is referred to as smart door lock which is more typically used in residential applications. Devices such as smart door locks are often battery powered, and power consumption and battery lifetime can be key parameters for the devices.

[0014] The Reader device 102 and the Access Controller 106 may communicate credential information using the Wiegand Protocol in addition to other communication protocols. In the Wiegand protocol, data is transmitted using a two-line, or two-wire interface between devices. Credential information is transmitted serially from the Reader device 102 to the Access Controller 106. For instance, the Reader device 102 may serially send a facility code and a user’s unique identification number to the Access Controller 106 according to the Wiegand protocol using the two-line interface. Wiegand communications typically involve analog, one-way signal transmissions over a pair of wires without encryption. Additional wires may be included to provide additional features. Benefits of a Wiegand system historically include simplicity and reliability, including in harsh environmental conditions. However, Wiegand also has recognized limitations, such as generally lacking an encryption protocol, which other communication protocols have sought to address. For example, OSDP typically provides bidirectional communication and encryption functionality, along with other examples of more complex functionality such as tamper monitoring, remote updates, biometric support, etc. OSDP systems generally provide digital data communications using formatted messages with one wire transmitting and the other wire receiving encrypted data. OSDP also typically utilizes RS-485 as the underlying communications protocol, which provide two differentially operated signal lines.

[0015] Nevertheless, some systems may include a mix of legacy and modern equipment or a mix of components of varying complexity. For example, a system owner may be in the process of upgrading equipment, or based on the design of the system, certain equipment may deploy high-security features while other equipment may only require medium- or lower-level security features. Certain devices may be manufactured to support multiple protocols, such as through physically separate buses and / or control circuitry. Accordingly, PAC systems utilize a number of protocols to communicate between components across the entire system, and certain devices may need to be able to communicate using a plurality of protocols for compatibility purposes.

[0016] In order to improve the ease of designing and deploying PAC systems in such scenarios, it is generally desirable to provide increased flexibility and compatibility betweenPAC system components. However, increased flexibility and compatibility often requires increased chip counts to support each of the various configurations and combinations of possible equipment through circuitry designed for that particular iteration. Therefore, it is desirable to minimize the number of components needed to implement a device interface, while still providing improved flexibility and compatibility for deployment in a variety of PAC system environments.

[0017] FIG. 2 is a block diagram of portions of an example of an access control system 200. The example system in FIG. 2 may be used to support Wiegand communications protocol in addition to other communications protocols, which preferably utilize the same or substantially the same communications circuitry. The system includes a Reader device 102 and an Access Controller 106. The Reader device 102 includes a transceiver circuit 210 and reader processing circuitry 212. The transceiver circuit 210 includes a differential drive output having two output terminals connected to a two-line network that connects the Reader device 102 and Access Controller 106. The two-line network may include twisted pair wire. The data placed on the two-line network by the transceiver circuit 210 is differential and the data output by one output terminal is complementary to the data output by the other output terminal. In certain examples, the transceiver circuit 210 includes an RS-485 type transceiver. The reader processing circuitry 212 can include one or more hardware processors executing instructions included in software or firmware to perform the functions described. To transmit data via the two-line serial interface, the processing circuitry 212 controls the output of the transceiver circuit 210.

[0018] Table 1 is a logic table for transmitting data with the transceiver circuit 210 in a standard implementation, such as with an RS-485 transceiver.

[0019] The logic table shows that the transceiver circuit 210 includes a data input (D) and a differential data output (A) and (B) where the B output is negative logic and is the complement of the A output. The transceiver circuit 210 also includes enable inputs. Activating the data enable (DE) input places the data signal at the data input D to the differential output. When the data enable is inactive, the differential drive output is in afloating or high impedance (High-Z) state. The two-line serial interface may include one or more pullup resistors (Rl, R2) that pull the lines to a predetermined pullup voltage when the output terminals of the differential drive output are in the high impedance state.

[0020] The transceiver circuit 210 includes a receive enable (RE*) that may be a low active input. If the link between the Reader device 102 and the Access Controller 106 is halfduplex, data will only be sent to the Access Controller 106 and the receive enable input is always disabled. For instance, if the Access Controller 106 provides the authentication of the credential information and controls access to the controlled area, the two-line serial interface may be a half-duplex link.

[0021] FIGS. 3 A and 3B are illustrations of examples of waveforms of the inputs and outputs of the transceiver circuit 210 to transmit data according to the Wiegand protocol. In FIG. 3 A, at time to, the receive enable of the transceiver circuit is inactive (or receive disabled) and the data enable is inactive (data input disabled). The data signal applied to the data input D is low or 0. As indicated in the logic table above, this typically indicates a state where the data signal is ignored and the outputs are in a floating or high impedance state. However, as described herein, transmission of Wiegand data may be accomplished using the same transceiver circuitry through the reader processing circuitry driving data signals out of this state. Because a low data signal is applied when the data input is disabled, the differential drive output of the transceiver circuit is disabled, and the pullup resistors pull the A and B outputs to the pullup voltage. This makes the data signals on the A and B outputs high or 1.

[0022] The reader processing circuitry 212 determines the data transmit time ti for transmitting a data bit to the Access Controller 106. At time ti, the processing circuitry 212 enables the differential drive output of the transceiver circuit 210 which causes output A to be driven to the data input of 0 and output B to be driven to the opposite of the data input or 1. The reader processing circuitry 212 maintains the data enable for the pulse width of the protocol (e.g., 40 microseconds or 40ps) until time t2 when the data enable is deactivated and the A and B outputs return to the high impedance state. The processing circuitry 212 determines the next bit time (e.g., 1 millisecond or 1ms) at time t3 and enables the differential drive output to place the next bit of data on the interface, which is also a 0. At time t4, the processing circuitry 212 applies a high data signal (or 1) to the data input D, and at time ts enables the differential drive output of the transceiver circuit 210 to place the 1 data bit on the interface.

[0023] In FIG. 3B, the receive enable of the transceiver circuit is active (or receive enabled) and the data enable is inactive. As indicated in the logic table above, this typicallyindicates a state where the data signal is again ignored and the outputs are in a floating or high impedance state. However, as described herein, transmission of Wiegand data may be accomplished using the same transceiver circuitry through the reader processing circuitry driving data signals of this state. The reader processing circuitry 212 enables or activates the data enable (DE) to drive data on the differential drive output of the transceiver circuit as similarly described above in the example of FIG. 3 A. Data received during times when the data enable is deactivated is ignored.

[0024] Returning to FIG. 2, the Access Controller 106 includes a receiver circuit 214 and controller processing circuitry 216. The receiver circuit 214 may be a standalone receiver or may be included in a transceiver circuit 218. The controller processing circuitry 216 receives data sent to the receiver circuit 214 by the Reader device 102 according to the Wiegand protocol. The controller processing circuitry 216 constructs the credential information from the received serial data. The controller processing circuitry 216 enables access to a controlled access area according to the data received from the Reader device 102. The controller processing circuitry 216 may enable access by unlocking a lock mechanism or may send a signal to a third device (not shown) to enable access to the credential holder in response to receiving appropriate credential data.

[0025] The Reader device 102 may include a card reader 220 and the reader processing circuitry receives credential data from the card reader to send to the Access Controller 106 via the two-line serial interface according to the Wiegand protocol. Alternatively, or in addition to the card reader 220, the Reader device 102 may include a wireless communication port 222 operatively coupled to the reader processing circuitry 212. The reader processing circuitry 212 receives credential data from the wireless communication port 222 to send to the Access Controller 106 via the two-line serial interface.

[0026] The circuits shown in the example of FIG. 2 can transfer data using other protocols as well. For example, the reader processing circuitry 212 may be configured (e.g., through programming) to transmit data according to the RS-485 protocol using the same hardware by enabling data and receive. Similarly, signaling using other protocols such as RS- 232 TTL may also be achieved through use of the same circuits shown in the example of FIG. 2 by enabling data and disabling receive.

[0027] FIG. 4 is an illustration of examples of waveforms of the inputs and outputs of the transceiver circuit 210 to transmit data in the access control system 200 according to the RS-485 protocol. In the example of FIG. 4, the data enable is always activated during the sending of data. The data applied to data input D immediately propagates to the differentialdrive output because the sending of data is always enabled. Single-ended versions of the protocols of the examples of FIGS. 3 and 4 can be implemented by not using the B output.

[0028] FIG. 5 is a flow diagram of a method of operating a Reader device (e.g., the Reader devices of FIG. 1 and FIG. 2) to communicate data via a two-line interface according to a Wiegand protocol. At block 505, the differential drive output of a transceiver circuit of the reader device is disabled prior to a data transmit time of the Wiegand protocol. The differential drive output may be disabled by inactivating a data enable of the transceiver circuit. The terminals of the differential output may both be at the same voltage when the differential drive output is disabled.

[0029] At block 510, a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential output is disabled. Because the differential output is disabled, the data signal is not propagated to the output of the transceiver circuit. At block 515, when it is time to transmit data, the differential drive output is enabled during the data transmit time to drive the data signal onto the two-line interface. At block 520, the differential output is disabled after the data transmit time.

[0030] The devices, systems and methods described herein can be used to communicate data according to multiple hardware protocols with a small amount of hardware. This reduces cost of the access control system and mitigates difficulty in procuring integrated circuits used in the Reader device and Access Controller.

[0031] FIG. 6 is a block diagram schematic of various example components of a device 600 for supporting the device architectures described and illustrated herein. The device 600 of FIG. 6 could be, for example, a reader device that receives credential information of authority, status, rights, and / or entitlement to privileges for the holder of a credential device. At a basic level, a reader device can include an interface (e.g., one or more antennas and Integrated Circuit (IC) chip(s)), which permit the reader device to exchange data with another device, such as a credential device, a card reader device, or an access controller device. One example of credential device is an RFID smartcard that has credential data stored thereon allowing a holder of the credential device to access a secure area or asset protected by the reader device and the access controller. Another example of credential device is a smartphone that stores the credential data and can send the credential data to the reader device and the access controller to access the secure area or asset.

[0032] With reference specifically to FIG. 6, additional examples of a reader device 600 for supporting the device architecture described and illustrated herein may generally include one or more of a memory 602, a processor 604, one or more antennas 606, acommunication port or communication module 608, a network interface device 610, a user interface 612, and a power source 614 or power supply.

[0033] Memory 602 can be used in connection with the execution of application programming or instructions by processing circuitry, and for the temporary or long-term storage of program instructions or instruction sets 616 and / or credential data 617, such as authorization data, credential authorization data, or access control data or instructions, as well as any data, data structures, and / or computer-executable instructions needed or desired to support the above-described device architecture. For example, memory 602 can contain executable instructions that are used by a processor 604 of the processing circuitry to run other components of device 600, to make access determinations based on authorization or credential data 617, and / or to perform any of the functions or operations described herein, such as the method of FIG. 5 for example. Memory 602 can comprise a computer readable medium that can be any medium that can contain, store, communicate, or transport data, program code, or instructions for use by or in connection with device 600. The computer readable medium can be, for example but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device. More specific examples of suitable computer readable medium include, but are not limited to, an electrical connection having one or more wires or a tangible storage medium such as a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), Dynamic RAM (DRAM), any solid-state storage device, in general, a compact disc read-only memory (CD-ROM), or other optical or magnetic storage device. Computer-readable media includes, but is not to be confused with, computer-readable storage medium, which is intended to cover all physical, non-transitory, or similar embodiments of computer-readable media.

[0034] Processor 604 can correspond to one or more computer processing devices or resources. For instance, processor 604 can be provided as silicon, as a Field Programmable Gate Array (FPGA), an Application-Specific Integrated Circuit (ASIC), any other type of Integrated Circuit (IC) chip, a collection of IC chips, or the like. As a more specific example, processor 604 can be provided as a microprocessor, Central Processing Unit (CPU), or plurality of microprocessors or CPUs that are configured to execute instructions sets stored in an internal memory 620 and / or memory 602.

[0035] Antenna 606 can correspond to one or multiple antennas and can be configured to provide for wireless communications between device 600 and another device. Antenna(s) 606 can be coupled to one or more physical (PHY) layers 624 to operate usingone or more wireless communication protocols and operating frequencies including, but not limited to, the IEEE 802.15.1, Bluetooth, Bluetooth Low Energy (BLE), near field communications (NFC), ZigBee, GSM, CDMA, Wi-Fi, RF, UWB, and the like. In an example, antenna 606 may include one or more antennas coupled to one or more physical layers 624 to operate using UWB for in band activity / communi cation and Bluetooth (e.g., BLE) for out-of-band (OOB) activity / communication. However, any RFID or personal area network (PAN) technologies, such as the IEEE 502.15.1, near field communications (NFC), ZigBee, GSM, CDMA, Wi-Fi, etc., may alternatively or additionally be used for the OOB activity / communication described herein.

[0036] Device 600 may additionally include a communication module 608 and / or network interface device 610. Communication module 608 can be configured to communicate according to any suitable communications protocol with one or more different systems or devices either remote or local to device 600. Network interface device 1010 includes hardware to facilitate communications with other devices over a communication network utilizing any one of a number of transfer protocols (e.g., Wiegand protocol, RS-485 protocol, 232TTL protocol, frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks can include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, wireless data networks (e.g., IEEE 802.11 family of standards known as Wi-Fi, IEEE 802.16 family of standards known as WiMax), IEEE 802.15.4 family of standards, and peer-to-peer (P2P) networks, among others. In some examples, network interface device 610 can include an Ethernet port or other physical jack, a Wi-Fi card, a Network Interface Card (NIC), a cellular interface (e.g., antenna, filters, and associated circuitry), or the like. In some examples, network interface device 610 can include a plurality of antennas to wirelessly communicate using at least one of single-input multipleoutput (SIMO), multiple-input multiple-output (MIMO), or multiple-input single-output (MISO) techniques. In some example embodiments, one or more of the antenna 606, communication module 608, and / or network interface device 610 or subcomponents thereof, may be integrated as a single module or device, function or operate as if they were a single module or device, or may comprise of elements that are shared between them.

[0037] User interface 612 can include one or more input devices and / or display devices. Examples of suitable user input devices that can be included in user interface 612 include, without limitation, one or more buttons, a keyboard, a mouse, a touch-sensitivesurface, a stylus, a camera, a microphone, etc. Examples of suitable user output devices that can be included in user interface 612 include, without limitation, one or more LEDs, an LCD panel, a display screen, a touchscreen, one or more lights, a speaker, etc. It should be appreciated that user interface 612 can also include a combined user input and user output device, such as a touch-sensitive display or the like.

[0038] Power source 614 can be any suitable internal power source, such as a battery, capacitive power source or similar type of charge-storage device, etc., and / or can include one or more power conversion circuits suitable to convert external power into suitable power (e.g., conversion of externally supplied AC power into DC power) for components of the device 600. Device 600 can also include one or more interlinks or buses 622 operable to transmit communications between the various hardware components of the device. A system bus 622 can be any of several types of commercially available bus structures or bus architectures.ADDITIONAL DISCLOSURE AND EXAMPLES

[0039] Example 1 includes subject matter (such as a reader device of an access control system) comprising a transceiver circuit and processing circuitry. The processing circuitry is configured to disable a differential drive output of the transceiver circuit, determine a data transmit time of a Wiegand protocol, apply a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential drive output is disabled, enable the differential drive output during the data transmit time, and disable the differential drive output of the transceiver circuit after the data transmit time.

[0040] In Example 2, the subject matter of Example 1 optionally includes the processing circuitry configured to send credential data to a separate device according to the Wiegand protocol using the transceiver circuit.

[0041] In Example 3, the subject matter of Example 2 optionally includes a card reader, and the processing circuitry is optionally configured to receive the credential data from the card reader.

[0042] In Example 4, the subject matter of one or both of Examples 2 and 3 optionally includes a wireless communication port operatively coupled to the processing circuitry, and the processing circuitry is optionally configured to receive the credential data via the wireless communication port.

[0043] In Example 5, the subject matter of one or any combination of Examples 1-4 optionally includes the transceiver circuit operatively coupled to a two-line serial interface,and the processing circuitry is optionally configured to send data to a separate device according to the Wiegand protocol on the two-line serial interface.

[0044] In Example 6, the subject matter of one or any combination of Examples 1-5 optionally includes a pullup circuit connected to terminals of the differential drive output of the transceiver circuit, and the pullup circuit is configured to set the terminals of the differential drive output to a pull up voltage when the differential drive output is disabled.

[0045] In Example 7, the subject matter of one or any combination of Examples 1-6 optionally includes a receive enable of the transceiver circuit being disabled.

[0046] Example 8 includes subject matter (such as a method of operating a reader device to communicate data according to a Wiegand protocol) or can optionally be combined with one or any combination of Examples 1-7 to include such subject matter, comprising disabling a differential drive output of a transceiver circuit of the reader device prior to a data transmit time of the Wiegand protocol, applying a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential output is disabled, enabling the differential drive output during the data transmit time, and disabling the differential drive output after the data transmit time.

[0047] In Example 9, the subject matter of Example 8 optionally includes enabling the differential drive output to transmit credential data to an access controller device according to the Wiegand protocol.

[0048] In Example 10, the subject matter of Example 9 optionally includes disabling a receive enable of the transceiver circuit when communicating with the access controller device according to the Wiegand protocol.

[0049] In Example 11, the subject matter of one or both of Examples 8 and 9 optionally includes enabling the differential drive output during the data transmit time of the Wiegand protocol to send credential data on a two-line serial interface to an access controller device according to the Wiegand protocol.

[0050] In Example 12, the subject matter of Example 11 optionally includes providing, by the access controller device, access to a resource in response to receiving the credential data on the two-line interface.

[0051] In Example 13, the subject matter of one or any combination of Examples 8- 12 optionally includes setting both terminals of the differential drive output to a pullup voltage when disabling the differential drive output.

[0052] Example 14 includes subject matter (such as an access control system) or can optionally be combined with one or any combination of Examples 1-13 to include suchsubject matter, comprising an access controller device and a reader device. The access controller device includes a receiver circuit and controller processing circuitry operatively coupled to the receiver circuit. The control processing circuitry is configured to receive data via the receiver circuit according to a Wiegand protocol and enable access to a controlled access area according to the received data. The reader device includes a transceiver circuit and reader processing circuitry operatively coupled to the transceiver circuit. The reader processing circuitry is configured to disable a differential drive output of the transceiver circuit, determine a data transmit time of the Wiegand protocol, apply a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential drive output is disabled, enable the differential drive output during the data transmit time, and disable the differential drive output of the transceiver circuit after the data transmit time.

[0053] In Example 15, the subject matter of Example 14 optionally includes the transceiver circuit and the receiver circuit being included in a two-line serial interface of the reader device and the access controller device.

[0054] In Example 16, the subject matter of Example 15 optionally includes a pullup circuit coupled to the two-line serial interface and configured to set the terminals of the differential output to a pull up voltage when the differential drive output of the transceiver circuit is disabled.

[0055] In Example 17, the subject matter of one or both of Examples 15 and 16 optionally includes the terminals of the differential output of the transceiver circuit being in a high impedance state when the differential drive output of the transceiver circuit is disabled.

[0056] In Example 18, the subject matter of one or any combination of Examples 14-17 optionally includes a card reader, and the reader processing circuitry is configured to receive credential data from the card reader and send the credential data to the access controller according to the Wiegand protocol.

[0057] In Example 19, the subject matter of one or any combination of Examples 14-18 optionally includes a wireless communication port operatively coupled to the reader processing circuitry. The reader processing circuitry is optionally configured to receive credential data via the wireless communication port, and send the credential data to the access controller according to the Wiegand protocol.

[0058] In Example 20, the subject matter of one or any combination of Examples 14 -19 optionally includes the reader processing circuitry optionally configured to disable a receive enable of the transceiver circuit when communicating data according to the Wiegand protocol.

[0059] In Example 21, the subject matter of one or any combination of Examples 14- 19 optionally includes the reader processing circuitry optionally configured to activate a receive enable of the transceiver circuit when sending data to the controller device and ignore data received at the transceiver circuit.

[0060] These Examples can be combined in any permutation or combination. The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, the subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

WHAT IS CLAIMED IS:

1. A reader device comprising: a transceiver circuit; and processing circuitry configured to: disable a differential drive output of the transceiver circuit; determine a data transmit time of a Wiegand protocol; apply a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential drive output is disabled; enable the differential drive output during the data transmit time; and disable the differential drive output of the transceiver circuit after the data transmit time.

2. The reader device of claim 1, wherein the processing circuitry is configured to send credential data to a separate device according to the Wiegand protocol using the transceiver circuit.

3. The reader device of claim 2, including: a card reader; and wherein the processing circuitry is configured to receive the credential data from the card reader.

4. The reader device of claim 2, including: a wireless communication port operatively coupled to the processing circuitry; and wherein the processing circuitry is configured to receive the credential data via the wireless communication port.

5. The reader device of claim 1, wherein the transceiver circuit is operatively coupled to a two-line serial interface; and wherein the processing circuitry is configured to send data to a separate device according to the Wiegand protocol on the two-line serial interface.

6. The reader device of claim 1, including:a pullup circuit connected to terminals of the differential drive output of the transceiver circuit, wherein the pullup circuit is configured to set the terminals of the differential drive output to a pull up voltage when the differential drive output is disabled.

7. The reader device of any one of claims 1-6, wherein a receive enable of the transceiver circuit is disabled.

8. A method of operating a reader device to communicate data according to a Wiegand protocol, the method comprising: disabling a differential drive output of a transceiver circuit of the reader device prior to a data transmit time of the Wiegand protocol; applying a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential output is disabled; enabling the differential drive output during the data transmit time; and disabling the differential drive output after the data transmit time.

9. The method of claim 8, wherein the enabling the differential drive output of the transceiver circuit includes enabling the differential drive output to transmit credential data to an access controller device according to the Wiegand protocol.

10. The method of claim 9, including disabling a receive enable of the transceiver circuit when communicating with the access controller device according to the Wiegand protocol.

11. The method of claim 8, wherein the enabling the differential drive output includes enabling the differential drive output during the data transmit time of the Wiegand protocol to send credential data on a two-line serial interface to an access controller device according to the Wiegand protocol.

12. The method of claim 11, including providing, by the access controller device, access to a resource in response to receiving the credential data on the two-line interface.

13. The method of any one of claims 8-12, including setting both terminals of the differential drive output to a pullup voltage when disabling the differential drive output.

14. An access control system, the system comprising: an access controller device including: a receiver circuit; controller processing circuitry operatively coupled to the receiver circuit and configured to: receive data via the receiver circuit according to a Wiegand protocol; and enable access to a controlled access area according to the received data; and a reader device including: a transceiver circuit; and reader processing circuitry operatively coupled to the transceiver circuit and configured to: disable a differential drive output of the transceiver circuit; determine a data transmit time of the Wiegand protocol; apply a data signal to be transmitted to a data input terminal of the transceiver circuit when the differential drive output is disabled; enable the differential drive output during the data transmit time; and disable the differential drive output of the transceiver circuit after the data transmit time.

15. The system of claim 14, wherein the transceiver circuit and the receiver circuit are included in a two-line serial interface of the reader device and the access controller device.

16. The system of claim 15, including: a pullup circuit coupled to the two-line serial interface and configured to set terminals of the differential output to a pull up voltage when the differential drive output of the transceiver circuit is disabled.

17. The system of claim 15, wherein terminals of the differential output of the transceiver circuit are in a high impedance state when the differential drive output of the transceiver circuit is disabled.

18. The system of claim 14, wherein the reader device includes: a card reader; andwherein the reader processing circuitry is configured to: receive credential data from the card reader; and send the credential data to the access controller according to the Wiegand protocol.

19. The system of claim 14, wherein the reader device includes: a wireless communication port operatively coupled to the reader processing circuitry; and wherein the reader processing circuitry is configured to: receive credential data via the wireless communication port; and send the credential data to the access controller according to the Wiegand protocol.

20. The system of any one of claims 14-19, wherein the reader processing circuitry is configured to disable a receive enable of the transceiver circuit when communicating data according to the Wiegand protocol.

21. The system of any one of claims 14-19, wherein the reader processing circuitry is configured to activate a receive enable of the transceiver circuit when sending data to the controller device and ignore data received at the transceiver circuit.

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