B&B 485OT9L Optically Isolated Serial Converter RS-232 to 422 or 485
The RS-232 port has a DB9 female connector with pins 3 (TD), 2 (RD), and 5 (Signal Ground) supported, pins 7 (RTS) and 8 (CTS) are tied together, and pins 6 (DSR), 1 (CD), and 4 (DTR), are also tied together. The 485OT9L has two LEDs: a Transmit Data LED showing when data goes from the RS-232 side to the RS-485 side, and a Receive Data LED showing data going from the RS-485 side to the RS-232 side. These are very useful for determining if data is getting through the converter. The RS-485 terminal blocks support Transmit Data (A) and (B), Receive Data (A) and (B), and Signal Ground. A single supply voltage to 30 VDC on the RS232 side powers the unit. An 8-position dipswitch allows the selection of baud rate, or 4-wire mode, echo on or off, and termination in or out.
The 485OT9L uses either RTS Control or Send Data Control to enable the RS-485 driver. This option is user selectable by setting push-on jumpers located next to the terminal blocks. RTS controls the driver using toggling Request to Send (pin 7) of the RS232 side. Raising RTS enables the driver and lowering RTS disables it. Automatic Send Data Control recognizes the first bit of data from the RS-232 side, enables the transmitter and disables the receiver. After the last bit of data is sent from the RS-232 side, the 485OT9L waits one character length then disables the transmitter and enables the receiver. The timeout can be selected with dipswitches or by changing the value of R21 (see Table 1). The timeout is preset at the factory for 9600 baud. Removing both sets of jumpers completely will constantly enable the RS-485 driver. This makes the 485OT9L behave like an RS-422 converter. See Table 2 for standard communications settings.
Termination resistance can be selected with Switch 8 for high baud rates and long cable distances. See B&B Electronics RS422/485 Application Note for more information (available on the web site or request one by mail). The 4-wire/2-wire switches (6 and 7) are turned off for 4-wire mode and on for 2-wire mode. When they are set on, they connect TD(A) to RD(A) and TD(B) to RD(B) internally. Switch 5 controls Echo on and off. When switch is in the off position the receiver is constantly enabled. Placing the switch in the on position allows the driver or the receiver to be enabled at any time. In 2-wire mode it is recommended that switch 5 be turned on to prevent data being sent out from "echoing" back through the receiver. to 32 receivers can be driven by any one RS-485 driver, allowing you to put together large systems with many drop points. Using an RS-422/485 repeater manufactured by B&B Electronics can increase the number of receivers. Table 1. Baud Rate Selection Baud Switch 1 OFF ON OFF Switch 2 OFF ON OFF Switch 3 OFF ON OFF ON OFF Switch 4 OFF ON OFF 820k 410k Not Used Not Used Not Used Not Used Not Used 8.2k Time out (ms)
This product designed and manufactured in USA of domestic and imported parts by
Communication Mode RS-422 Mode (full duplex) RS-485 4-Wire Mode (full-duplex) RS-485 2-Wire Mode (half-duplex) JP1 Neither RTS or SD RTS or SD Switch 5 Echo OFF ON Switch 6 4W/2W OFF ON Switch 7 4W/2W OFF ON
