Serial Connections

The Iron Pi features two industrial serial ports: one RS-485 port, and one RS-232 port. Additionally, there is a TTL serial console port intended for diagnostic and recovery use.

RS-485 Port

The RS-485 port is located on the Iron Pi's main terminal block. It is accessible in the Iron Pi's OS as /dev/ttySC0. A JCore-provided service called rs485-config runs at boot time and configures the port for half duplex operation. User applications can then access the port like any other Linux serial port.

RS-485 is a three wire standard. RS-485 A and RS-485 B are a differential signal pair, and a signal ground connection is required between the Iron Pi and all connected RS-485 devices.

The Iron Pi has an internal 130 ohm bus termination resistor, as well as 620 ohm pull-up and pull-down resistors to keep the bus in a known state when no devices are transmitting. You should ensure that the end of the bus opposite the Iron Pi also has a 130 ohm termination resistor. Some devices have a fixed or switchable built-in termination resistor, while other devices require you to connect an external termination resistor.

Make sure that you only have two total termination resistors on your RS-485 bus, including the one built into the Iron Pi! Adding more termination resistors will degrade the signal quality and cause communication errors.

RS-232 Port

The RS-232 port is located on the Iron Pi's main terminal block. It is accessible in the Iron Pi OS as /dev/ttySC1. The RS-232 port supports full duplex operation, meaning the Iron Pi and the remote device can both be transmitting simultaneously.

Unlike RS-485, RS-232 is not a multi-drop standard, so you can only connect the Iron Pi to one remote device via RS-232.

When connecting a remote device to the Iron Pi's RS-232 port, connect the remote device's transmit terminal to the Iron Pi's receive terminal, and connect the remote device's receive terminal to the Iron Pi's transmit terminal. Connect the remote device's signal ground to the Iron Pi's signal ground.

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