DESCRIPTION AND OPERATION
UNIVERSAL I/O EXPANDER BUS INTERFACE
2 - 6
WBPEEUI240755B0
®
connects the bus between the control and I/O modules. Cable
assemblies can extend the bus to six MMUs.
A control module and its I/O modules form an individual sub-
system within a process control unit (PCU). The I/O expander
bus between control module and I/O module subsystems
must be separated. Leaving a dipshunt socket empty or not
connecting the MMUs with cables separates them.
UNIVERSAL I/O EXPANDER BUS INTERFACE
The CIS and QRS modules use a custom gate array to perform
the I/O expander bus interface function. All the control logic
and communication protocol are built into an integrated cir-
cuit (IC). This IC provides the following functions:
•
Address comparison and detection.
•
Function code latching and decoding.
•
Read strobe generation.
•
Data line filtering of bus signals.
•
On-board bus drivers.
MODULE DATA
Function Code (FC) 79 in the MFP configuration accesses the
CIS or QRS module on the I/O expander bus. It also allows the
MFP to automatically read input data or status data from the
I/O module, and write output data to it. This data is output by
buffer circuits to the I/O expander bus interface (Fig.
). The
I/O module address in FC 79 must be the same as the address
set on I/O address dipswitch (S1).
I/O Data
I/O data is analog input, digital input, and digital and analog
output readback values that the MFP reads from the I/O mod-
ule. It is also analog and digital output values that the MFP
sends to the module. The MFP uses this data to monitor and
control a process, and verify I/O module operation.
Analog input data consists of analog counts from the A/D con-
verter. Analog counts are digital values that correspond to
analog signals; the A/D performs the conversion. The signals
converted include the four analog inputs, two reference volt-
ages (1 VDC and 5 VDC) and two analog output readback val-
ues. The MFP reads each of these count values once every
execution cycle. Each analog input count value corresponds to
an analog input voltage. Reference voltage values are read by
the MFP to verify A/D converter integrity. It reads the two ana-
log output values to adjust the analog outputs and check for
output circuit failures.
