Rockwell Automation 1771-DB BASIC MODULE User Manual
Page 41
Chapter
Using the Communication Ports
2
2 -3
PRT1 and PRT2 Transmit and Receive Buffers
Ports PRT1 and PRT2 each have a 256-character receive (input) buffer and
a 256-character transmit (output) buffer. Data in these buffers are
monitored by circular queues. If a queue detects that a buffer is full (i.e.,
the buffer has 256 characters waiting to be serviced), and handshaking is
enabled (software or hardware), then the queue does not allow new
characters to enter the buffer until existing characters have been serviced
and room is available for the new characters.
DH485 Port
The DH485 port uses the DH-485 communication mode to communicate
with SLC processors. The DH485 port has an RJ-45 connector. Use the
standard Allen-Bradley cables (cat. no. 1747-C10,1747-C11, 1747-C20)
for all DH-485 interconnects.
The DH485 port is not electrically isolated.
20376–M