Hardware Handshaking - Allen-Bradley SLC 500 BASIC User Manual

3-8 Installing and Wiring Your Module
Publication 1764-UM001A-US-P
Table 3.1 Ports PRT1 and PRT2 Pin Assignments
Pin RS-232/423
1 Note 1
2 RXD
3 TXD
4 DTR
5 COMMON
6 DSR
7 RTS
8 CTS
9 (1)
(1) In RS-423 mode, these pins are still connected to their RS-422 loads. Do not use these pins in RS-423
mode.
(2) In RS-422 and RS-485 modes these pins are connected to their RS-423 drivers and receivers. Do not use
these pins in either RS-422 or RS-485 mode.
(3) In RS-485 mode, these pins are still connected to their RS-422 receivers. Do not use these pins in RS-485
mode.
Wiring diagrams for the RS-232/423 communication mode are shown starting on
page 3-10.

Hardware Handshaking

The module uses the following rules when hardware handshaking is enabled. The
module:
• does not transmit until CTS becomes active
• examines DSR following the receipt of a character. If the DSR is active, the
character is placed in the input queue. If DSR is inactive, the character is
assumed to be noise and is discarded.
RS-422 RS-485
422 TXD - TRXD -
422 RXD - (3)
(2) (2)
(2) (2)
COMMON COMMON
422 RXD +
(3)
(2) (2)
(2) (2)
422 TXD + TRXD +
IBM AT Standard
RS-232 Signals
DCD or CD
RXD
TXD
DTR
COMMON
DSR
RTS
CTS
RI