The 485CSP2 converts unbalanced RS-232 signals to balanced, full or halfduplex RS-485 signals. It also provides transient surge protection and fast acting fuses on the RS-485 data lines. RS-485 is an enhanced version of the RS-422 Standard. It allows multiple drivers and receivers on a two-wire system.
The RS-232 port has a female DB-25 connector with pins 2 (TD), 3 (RD), and 7 (Signal Ground) supported. Pins 4 (RTS) and 5 (CTS) are tied together, and pins 6 (DSR), 8 (CD), and 20 (DTR) are also tied together. Pins 1 (Frame Ground) and 7 (Signal Ground) are connected straight through to the RS-485 terminal blocks. The 485CSP2 has two LEDs, a Transmit Enable LED to show when the RS-485 driver is enabled, and a Receive Data LED showing data appearing at pin 3 of the RS-232 port. These are very useful for determining if data is getting through the converter. Note that the Transmit Enable LED indicates only that the 485 driver is enabled, data must be present on pin 2 of the 232 side for data to be transmitted out of the 485 side. If no data is present, no data will be transmitted even though the Transmit Enable LED is illuminated. The RS-485 terminal blocks support Transmit Data (A) and (B), Receive Data (A) and (B), Frame Ground, Signal Ground, and +12 VDC input. See Figure 1.
For the protection properties on the 485CSP2 to work, the Frame Ground terminal block or pin 1 on the RS-232 side must be connected directly to a good frame (chassis, green wire, or earth) ground. This must be a low impedance connection for the 485CSP2 to be effective.
