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3.3.18 COM Port Header
Dual RS-232/RS-422/RS-485 pin header- CN25
Pin
Signal RS-232 mode
1
COM0_RxD
COM0_Rx+
2
COM2_RxD
COM2_Rx+
3
COM0_TxD
COM0_Tx-
4
COM2_TxD
COM2_Tx-
5
GND
GND
7
COM0_RTS#
COM0_Tx+
8
COM2_RTS#
COM2_Tx+
9
COM0_CTS#
COM0_Rx-
10
COM2_CTS#
COM2_Rx-
CN23 position
Not inserted
Please be aware that for proper RS-485 working, the RTS# signals must be used as a handshaking signal, i.e. it is used to control the data flow direction. When
RTS# signal is driven low, then the RS-485 port is in receiving mode, when RTS# signal is driven high then the RS-458 port is in transmitting mode.
The port referenced as COM0 is the transceivered signal from the SMARC
from the SMARC
®
module SER#2 interface.
Signals Description:
COM0_RxD/COM2_RxD: COM port #0 / #2 RS-232 Receive data,
COM0_TxD/COM2_TxD: COM port #0 / #2 RS-232 Transmit data
CSM-B79
CSM-B79 User Manual - Rev. First Edition: 1.0 - Last Edition: 1.1 - Author: A.R - Reviewed by S.R. - Copyright © 2021 SECO S.p.A.
Signal RS-422 mode
Signal RS-485 mode
COM0_Data-
COM2_Data-
GND
COM0_Data+
COM2_Data+
COM Port #0 mode
1-2
RS-422
2-3
RS-232
RS-485
According to SMARC
a maximum of four asynchronous serial ports on the card edge connector,
two of them complete of Flow control RTS# and CTS# signals (SER#0 and
SER#2), the other with only Tx and Rx signals (SER #1 and SER #3).
SER#0 and SER#2 ports are managed through multistandard (RS-232/RS-
422/RS-485) transceivers, and the output is available on an internal 9-pin
standard male pin header, p 2.54 mm, 5+4 pin, h= 6mm, type NELTRON
p/n 2213S-10G-E06 or equivalent.
The selection of the kind of interface (RS-232, RS-422 or RS-485) can be
made by using 3-way jumpers CN23 and CN24.
CN24 position
COM Port #2 mode
1-2
RS-422
2-3
RS-232
Not inserted
RS-485
®
module SER#0 interface, while the port referenced as COM2 is the transceivered signal
®
Rel. 2.1.1 specification, SMARC
®
modules foresee
64
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