Page 242 - Embedded Microprocessor Systems Real World Design

+24 V

PULLUP
Open Collector

Master

Comparator
Common serial
party line
PORTBIT 4 ~~~~~~N
Comparator
Open Collector

TX . I
Rx

Comparator

Open Collector
-
Tx
Rx
Comparator /
c ,
Open Collector 12V zener
PORT BIT

Figure 8.11
Serial, Asynchronous Communication with Attention Request Feature.

need some additional hardware to isolate them since both boards will come up in
standard mode with the output drivers enabled.
A single printer port can be used to communicate between a master CPU and
numerous slaves. If you implement such an interface, be sure that only one device
at a time drives the data bus.

Multiprocessor Systems 223