Connecting modem via serial interface
The AM-201 can be used with either an RS485 or RS232 serial interface. To control the modem it is necessary to use AT commands. Regardless of the type of serial interface, the commands are the same.
Connecting a modem via RS485
To connect the modem to the device via RS485 serial interface, connect according to the following diagram.
Always connect the modem's A signal to the host's A signal, and the modem's B signal to the host's B signal. Most of the time it is not necessary to connect the common ground, or G, signal, but it is good practice to connect it.
Connecting a modem via RS232
To connect the modem to the device via RS232 serial interface, connect according to the following diagram.
Remember that the modem's RX signal is combined with the host's TX signal, and the modem's TX signal is combined with the host's RX signal. That is, the signals are crossed. It is also necessary to connect common ground, or G.