All the Sequent Microsystems cards with the exception of the Home Automation have an RS485 transceiver wired to a pluggable connector. The cards fall into two categories: Smart (with local processor) or Dumb (using I/O expanders).
Using the RS485 port on the Smart cards
On the Smart cards (Industrial and Building Automation, and RTD Data Acquisition), a 2 section jumper permits connecting the RS485 port directly to the processor or to Raspberry Pi.
To use the port from Raspberry Pi, perform the following steps:
- Install two jumpers to route the RS485-TX and RS485-RX from the line driver to Raspberry Pi GPIO connector
- Disable the RS485 port on the local processor
- Activate the serial port on Raspberry Pi from raspi-config command.
- Install an USB to RS485 adaptor on your PC.
- Install a terminal emulator program on your PC.
- Click HERE to download a Python script to test the communication.
You can also use the RS-485 port from the local processor, by removing the jumpers and using the following commands:
Using the RS485 port on the Dumb cards
On the Dumb cards (8-RELAY, 8-MOSFET, 8-INPUTS, 4-RELAY/4-INPUTS and 16-INPUTS) the RS485 port is connected directly to Raspberry Pi serial port. The RX line is separated by a single jumper, labeled either RS485 or RXD. Install the jumper if you want to use the RS485, remove it if you need to use the RXD pin as GPIO