Jameco Electronics Rabbit 3000 - Manual (Page 193)

184 Rabbit 3000 Microprocessor
answer its interrupts within 20 µs. There will be no slow down if the receiver can answer
its interrupt within 1/2 clock or 1.25 µs. If it can answer within 1.5 clocks, or 2.75 µs, the
data rate will slow to 44,444 bytes per second. If it can answer in 2.5 clocks or 6.25 µs,
the data rate slows to 40,000 bytes per second. If it can answer in 3.5 clocks or 8.75 µs,
the data rate will slow to 36,363 bytes per second, and so forth.
If two-way half-duplex communication is desired, the clock can be turned around so that
the receiver always provides the clock. This is slightly more complicated since the
receiver cannot initiate a message. If the receiver attempts to receive a character and the
transmitter is not transmitting, the last bit sent will be received for all eight bits.