ABB Symphony Harmony Series Instruction page 58

Digital I/O Buffer
I/O Circuit Connections
I/O Expander Bus
I/O Expander Bus Interface
WBPEEUI240769B0
The digital I/O buffer block is a buffer and register that holds
the values of the digital inputs and outputs. The I/O expander
bus interface writes digital data to the register for output by
the driver block circuits, and reads the digital input values
from the buffer.
The I/O signals connect to the 30-pin card edge connector P3
of the I/O modules using a termination cable from a termina-
tion unit. It also supplies +24 VDC power to operate the analog
output circuits.
The I/O expander bus is a high speed synchronous parallel
bus. It provides a communication path between the controller
and the I/O modules. The controller provides the control func-
tions and the I/O module provides the input/output functions
to and from the controller. The P2 card edge connector of the
I/O module and controller connects to the bus.
The I/O expander bus is parallel signal lines located on the
module mounting unit backplane. A 12-position dipshunt
placed in a connection socket on the module mounting unit
backplane connects the bus between the controller and I/O
modules. Cable assemblies can extend the bus to six module
mounting units.
A controller and its I/O modules form an individual subsystem
within a process control unit. The I/O expander bus between
the controller and the I/O module subsystems must be sepa-
rated. Leaving a dipshunt socket empty or not connecting the
module mounting unit with cables separates them.
The I/O modules use a custom gate array to perform the I/O
expander bus interface function. All the control logic and com-
munication protocol are built into an integrated circuit.
I/O Circuit Connections
2 - 7