Multi-Channel Serial Ports

Both the DS1101 and DS1102 have a single DB9 connector but offer several RS232 channels . We define a serial channel as including at least the RX and TX signals. The standard serial port has six "important" signals: RX, TX, CTS, RTS, DSR, and DTR. The CTS/RTS and DSR/DTR signal pairs of the DS1101 and DS1102 can alternatively be used as independent serial channels RX2/TX2 and RX3/TX3. If your Modbus device does not require any other signals but RX and TX (as is usually the case), then a single controller can give you three independent RS232 channels! This applies to the DS1101, as well as DS1102 in the RS232 mode. The DS1102 only offers a single channel in the RS485 mode.

RS232 Mapping Options (DS1101 and DS1102)

Tibbo has defined 15 port mapping options (channel arrangements). These are our standard mapping options that we use for all apps that run on DS1101 and DS1102 devices.

As you can see, both the DS1101 and DS1102 have at least three channels: RX/TX, RX2/TX2 (CTS/RTS), and RX3/TX3 (DSR/DSR). The DS1101 additionally has the RX4 line but no TX4. Since Modbus applications require both the RX and TX lines, you can disregard this "half-channel."

Of all the options presented in the table above, two stand out as "very useful" for the Modbus Gateway app:

• Option 0 , because it represents the standard serial port arrangement.

• Option 8 , because it offers three simple serial channels with just the RX and TX lines in each channel (which is usually enough for Modbus devices).

RS422 and RS485 (DS1102 only)

You can only use the mapping option 0 in these modes.