Page 241 - Embedded Microprocessor Systems Real World Design
P. 241
+12 v
PULLUP
Open Collector
Master
TX
Rx
Comparator
Common serial
party line
Open Collector
Tx
Rx
Comparator
-
Open Collector
TX
Rx
Comparator
Figure 8.10
Serial, Asynchronous Communication.
communicates using only four of the data lines because the data lines on the stan-
dard printer port are unidirectional, output only. You cannot tie the data lines of
two printer ports together or you will get bus contention. However, many mod-
ern printer ports support various bidirectional modes of operation. You could use
this capability to get full 8-bit-wide transfers between two computer boards, but you
222 Embead Micropomsor Systents
