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. See "Advanced configuration" below
for alternative configurations.
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
RS-485 JUMPERS POSITION
21
Strato Pi UPS User Guide
