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(-)
