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12 Documentation Number 232D4SS84502 Manual
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
There are two components located in the port B circuit area on
the main printed circuit board, a resistor (R75) and a capacitor (C4),
that are part of the send data control circuit. These components are
factory selected for 9600 baud, which allows the send data control
to operate at 9600 baud or higher. With these two components the
RS-485 driver will be disabled approximately 1 millisecond after the
last character has been sent. To change to a baud rate lower than
9600 baud, or to configure the send data control to match a specific
baud rate, change R75 and C4 to the value specified in Table 6.
Use Figure 3 to locate R75 and C4. Note that these timing
components are not used when the handshake control method is
selected.
To configure a port for RS-485 two-wire mode, both jumpers
must be placed in the two-wire "2" position for the corresponding
port Refer to Figure 4 for these jumper locations. The TD (A) and
RD (A) lines need to be connected together; also the TD (B) and RD
(B) lines need to be connected to each other. Giving you a Data (A)
line and a Data (B) line. “A” being “+” and “B” being “-”.
Handshake control (RTS) requires that the software use a
handshake signal to enable/disable the RS-485 driver. The
handshake signal RTS (pin 4) is used when the Master port is
configured as a DCE port and CTS (pin 5) is used when the Master
port is configured as a DTE port. If the RTS option is needed,
contact B&B technical support for details.
Table 6. Component Values For Send Data Timing
Baud
Rate
Time (ms) Resistor Value
R75 (ohms)
Capacitor Value
C4(microfarads)
300
33.3 330K .1
600
16.6 160K .1
1200
8.33 820K 0.01
2400
4.16 430K 0.01
4800
2.08 200K 0.01
9600
1.04 100K 0.01
19200
0.520 56K 0.01
38400
0.260 27K 0.01
56700
0.176 16K 0.01
115200
0.0868 8.2K 0.01