B&B Electronics 3PCIOSD2A, Manual

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Documentation Number 3PCIOSD2x-3903 Manual Chapter 2 11
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
B&B Electronics Ltd – Westlink Comm. Pk. – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445
PORT 1 JP3
A 232
B 232
C 232
D 232
422/ 485
422/ 485
422/ 485
422/ 485
PORT 1
TX 422
RX 422
I N
485
485
OUT
PORT 2
A 232
B 232
C 232
D 232
422/ 485
422/ 485
422/ 485
422/ 485
CONTROL
RTS ( 232)
RTS ( 232) SD PORT 1
SD PORT 2
CLOCK
*4 *1
TERM I NATI ON
PORT 2
TX 422
RX 422
I N
485
485
OUT
TERM I NATI ON
JP4
JP6
JP5
JP2
JP1
CONNECTED
NO M EANI NG
Figure 4. RS-485 Mode Jumper Settings
Explanation of RS-485 Operation
In RS-485 mode the transmit driver must be enabled to transmit, and
set to a high impedance (tri-state) mode at the end of transmission.
In a 2-wire (half duplex) mode, the receiver is disabled during
transmit and enabled when not transmitting.
The 3PCIOSD2x card provides two methods of enabling/disabling
the transmit driver: automatic Send Data (SD) control and Request
To Send (RTS) control. With automatic SD control, the driver is
enabled when data is sent. The driver remains enabled for the
transmission time and ten data bits after data transfer is complete.
The SD circuit automatically adjusts its timing to the baud rate of the
data. With RTS control, software must assert the RTS line to enable
the driver and de-assert to disable the driver. To select SD control
for either port, place the JP2 "Port 1" or "Port 2" jumper in the “Send
Data” (right) position for that port. Place the jumper in the
“RTS(232)” (left) position for RTS control.
The receiver can also be enabled and disabled, a useful feature
in two-wire communications to prevent the transmitted data from
"echoing back" on its own receiver. The second jumper "RX" of JP4
(Port 1) or JP6 (Port 2) determines the receiver mode. If the
jumpers are placed in the “485” position, the "echo" is turned off.
This is achieved by disabling the receiver when the driver is
enabled. Placing the "RX" jumper in the “422” position will hold the
receiver enabled at all times.
More information on RS-422
communications can be found in B&B’s free
RS-422/485
Application Not e (available on our websites).