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RS-422 Connections
Manual Documentation Number: ESP904-0504 Appendix B 61
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
A
A
P
P
P
P
E
E
N
N
D
D
I
I
X
X
B
B
:
:
R
R
S
S
-
-
4
4
2
2
2
2
C
C
O
O
N
N
N
N
E
E
C
C
T
T
I
I
O
O
N
N
S
S
ESP904 DB-9 Pin-outs in RS-422 Mode
RS-422
Signal Name
Direction
RS-422
DB9M
Pin
Receive Data A (−) In RXDA (−) 1
Receive Data B (+) In RXDB (+) 2
Transmit Data B (+) Out TXDB (+) 3
Transmit Data A (−) Out TXDA (−) 4
Signal Ground --- GND 5
Clear to Send A (−) In CTSA (−) 6
Clear to Send B (+) In CTSB (+) 7
Request to Send B (+) Out RTSB (+) 8
Request to Send A (−) Out RTSA (−) 9
Figure 47. RS-422 Connections in a DB-9 Connector
RS-422 Connections
62 Appendix B Manual Documentation Number: ESP904-0504
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
Figure 48. 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
:
:
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(-)