B&B Electronics 232D4SS8 manual 1200, 2400, 4800, 9600, 19200, 38400, 56700, 115200

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.

Table 6. Component Values For Send Data Timing

Baud	Time (ms)	Resistor Value	Capacitor Value
Rate		R75 (ohms)	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

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.

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