3-2. BUS INTERFACE MODULE. Continued
The keyboard encoder converts keyboard switch closures into a hexadecimal code. When the microprocessor is
ready to read the keyboard, the code is put onto the data lines. The keyboard encoder also provides a debounce
function and a two-key-closure inhibit function.
The receivers and drivers form a data line transceiver. They transform serial data and clock signals from the
output buffer into balanced differential signal output to drive the rt interface bus. In receive, they transform the
balanced differential signals into BUS DATA and BUS CLOCK for the processor module.
A reset circuit generates a negative reset pulse at power turn-on. This is used to start the microprocessor at the
correct place in its program. A negative reset pulse is also generated whenever the TAKE CONTROL switch
changes. This starts the-microprocessor at the beginning of its program whenever relinquishing or taking control
of the rt. The reset circuit also holds the reset negative when LOW V RESET is present. LOW V RESET is present
when the +28V line drops to about +18V. LOW V RESET is supplied by the power supply.
Figure 3-2. Bus Interface Module Functional Block Diagram