Card Setup
Headers E8 (Port 1) and E10 (Port 2) are used to control the RS-485 mode functions for the driver circuit. The two selections are ‘RTS’ enable or ‘Auto’ enable. The ‘Auto’ enable feature automatically enables/disables the RS-485 interface. The ‘RTS’ mode uses the ‘RTS’ modem control signal to enable the RS-485 interface and provides backward compatibility with existing software products. If you have E3 and E9 in the RS-422 mode and wish to have the RTS signal present at the DB connector place a jumper over the RTS pins at E8 and E10. Otherwise the RTS control signal will not be present at the DB connector.
Headers E3 (Port 1) and E9 (Port 2) are used to control the RS-485 enable/disable functions for the receiver circuit and determine the state of the RS-422/485 driver. The RS-485 ‘Echo’ is the result of connecting the receiver inputs to the transmitter outputs. Every time a character is transmitted; it is also received. This can be beneficial if the software can handle echoing (i.e. using received characters to throttle the transmitter) or it can confuse the system if the software does not. These header blocks are described in the illustration and table that follow:
1 | | | | | | | |
| | No | | | | |
| | | | | | |
Echo Echo | 422 | 485 |
| | | E3 = Port 1 | | |
| | | E9 = Port 2 | | |
Position 1 ‘Echo’ | Echoes the data that is transmitted. |
| All characters transmitted are |
| received. (Only relevant in the two |
| wire RS-485 Mode) |
Position 2 ‘No Echo’ | Inhibits the data that has been |
| transmitted. Receiver is off when |
| transmitter is on. (Only relevant in |
| the two wire RS-485 Mode) |
Position 3 ‘422’ | RS-422/485 Driver always enabled |
| (RS-422 Mode). RTS modem control |
| signal available on DB-9 connector. |
Position 4 ‘485’ | RS-422/485 Driver enabled by RTS |
| or ‘Auto’ enabled. Modem control |
| signal not available on DB-9 |
| connector. |
