Technical data

RS-422 Connections
72 Appendix B Manual Documentation Number: ESP904-4513m
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone] – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph [phone] – Fax [phone] – www.bb-europe.com
Figure 64. RS-422 Connections with Flow Control
In the RS-422 mode, TXD lines are outputs and RXD lines are inputs.
Connect the ESP904 TXDB(+) line to the RXDB(+) line of the serial device,
and the ESP904 TXDA(-) to the RXDA(-) of the serial device.
If Flow Control is set for RTS/CTS, connect the ESP904 RTSB(+) to
CTSB(+) of the serial device and the ESP904 RTSA(-) line to the CTSA(-)
of the serial device. Connect from the ESP904 CTSB(+) line to the RTSB(+)
of the serial device and from the ESP904 CTSA(-) line to the RTSB(+) line
of the serial device.
If connecting to Receive Only RS-422 devices, connect from the ESP904
TXDB(+) and TXDA(-) lines to the receive pairs on all serial devices.
Ground is signal ground and provides a common mode reference for the RS-
422 Receiver and Transmitters.
N
N
o
o
t
t
e
e
:
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The RS-422 mode can be used for full duplex 4-wire RS-485 operation provided
that the ESP904 is acting as a sole master connecting to all the slave devices,
and all slave devices share the Receive signal lines to the master. Set Flow
Control for none, and omit connections to RTS/CTS line pairs.
ESP904 pin-out
in RS-422 mode
RS-422
Device
RS-422 Signal Names
DB-9
Pin#
Connections
Signal
Receive A (-)
RXDA(-)
1
TDA(-)
Receive B (+)
RXDB(+)
2
TDB(+)
Transmit B (+)
TXDB(+)
3
RDB(+)
Transmit A (-)
TXDA(-)
4
RDA(-)
Ground
GND
5
GND
Clear to Send A (-)
CTSA(-)
6
RTSA(-)
Clear to Send B (+)
CTSB(+)
7
RTSB(+)
Ready to Send B (+)
RTSB(+)
8
CTSB(+)
Ready to Send A (-)
RTSA(-)
9
CTSA(-)