A bidirectional
repeater and data
multiplexer for serial data comprises a plurality of comparators 302, 304, 306, 308 coupled to the respective input / output (I / O) terminals of a plurality of serial data
transceiver devices A1, A2, A3, A4 such as used in I2C communication. Also coupled to these I / O terminals is a plurality of active pulldowns 316, 318, 320, 322. The outputs of the comparators are coupled to N:1 Select 310 logic wherein the desired
data input is selected responsive to select lines S1, S2, S3, S4. The output of the N:1 select logic is coupled to a bidirectional
control circuit 210, which couples the selected data to the control terminal of an active pulldown 206 having its source coupled to a pulldown
voltage Vp low enough to represent a logic “low” level but non-zero, and a drain connected to the I / O terminal of a device B. Also connected to the I / O terminal of device B is an inverting
comparator having a
threshold voltage Vt somewhat below the pulldown
voltage Vp described above, such that the
comparator ignores the low level Vp of the active pulldown, but responds to the less than Vp data zero level from device B. This prevents data lockup where data from An would flow back to the same device An. The data output of
comparator 208 is thus a repeated version of data present on the I / O terminal of device B, and is coupled through 1:N Select 312 logic, responsive to the same select lines S1 . . . described above, to one of the plurality of active pulldowns 316, 318, 320, 322. Data from device An, one of the plurality of devices A1 . . . A4, is thus repeated and selectively routed to device B. Similarly, data from device B is selectively routed to the active pulldown coupled to the same device An. Pulldown voltages Vp and threshold voltages Vt may be varied to optimize
coupling with device B, as long as the pulldown
voltage Vp remains above the
threshold voltage Vt; the pulldown and threshold voltages may be selected from a plurality of such pulldown and threshold voltages, in order to optimize
noise margins when
coupling to devices having different Vil and Vol specifications.