Rain Bird IC System Design Manual page 7

Components of the Integrated Control Interface Plus (ICI+)
CPU Board
The CPU Board provides communication between the
Central Control computer and each of the driver boards.
The CPU board includes 3 different connections. For
normal operations the USB connections are used, the left
USB port is for Satellite equipment, the right USB port is
for IC System equipment. For a remote located ICI+
(running IC System products only) the Serial connection is
used with a MAXI Remote Location Kit (MRLK). The CPU
board will communicate based on whichever
communication protocol is selected, TWX or TWI. TWX is
for IC System and IFX hybrid communication, TWI is for
satellite system communication only.
Driver Board
The Driver Board provides communication between the CPU board and the
equipment in the field. The driver board has two 2-wire paths on each board.
Within an IC System each wire path controls a maximum of 750 ICM addresses.
This same wire path can also communicate with IFX connected satellites such as
the PAR+ES but may not exceed the limit of 750 stations per wire path.
IC System Design Guide, v2.4 7