Simply connect the RS-232 RX, TX and GND lines to the RS-232 posts of the Strato Pi
terminal block or the RS-485 A, B and GND to the RS-485 posts of the terminal block.
Never connect both RS-232 and RS-485 lines to Strato Pi. Strato implements a single
serial port, not two.
Both interfaces are isolated from the Raspberry Pi’s serial lines using dedicated opto-
couplers and from the main power supply with a high-efficiency DC-DC converter. This
configuration should prevent ground loops between devices connected through the serial
lines.
The RS-485 TX/RX switching is implemented automatically in the Strato Pi’s micro-
controller, based on speed and number of bits detection, and is completely transparent to
the software controlling the UART on Raspberry Pi. It can also be manually configured to
work with fixed communication parameters (speed, bits, parity, stop bits) or in passive
mode (refer to the "Strato Pi Logic Controller Advanced Configuration Guide" document for
additional information).
The RS-485 line has 620 Ohm pull-up and pull-down resistors on lines A and B. The
biasing resistors ensure that, during idle periods the data lines are kept at a stable voltage
level and prevent false triggering of receiver input.These resistors can be disabled by
removing jumpers JP1 and JP3 respectively.
A 100 Ohm termination resistor between A and B can be enabled installing jumper JP2.
RS-485 JUMPERS SCHEMATIC
21
Strato Pi Base User Guide
