DESCRIPTION AND OPERATION
MODULE DATA
2 - 6
I-E96-316A
®
MODULE DATA
Function Code (FC) 79 in the MFP configuration accesses the
QRS on the slave expander bus. It also allows the MFP to auto-
matically read input data or status data from the slave module,
and write output data to it. This data is output by buffer cir-
cuits to the slave expander bus interface (see Figure
). The
slave address in FC 79 must be the same as the address set on
the slave 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 QRS. It is
also analog and digital output values that the MFP sends to the
QRS. The MFP uses this data to monitor and control a process,
and verify QRS operation.
Analog input data consists of analog counts from the A/D con-
verter. Analog counts are digital values that correspond to ana-
log 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.
The MFP reads a one byte value that consists of digital output
readback values and digital input values. The digital input val-
ues indicate the digital input states. Each bit corresponds to
one input; the bit value reflects the state of that input, either
open (logic 0) or closed (logic 1). Digital output readback data
reflects the output states. The MFP uses this data to verify that
the outputs are correct. Each bit corresponds to one output; a
logic 1 indicates an active (ON) output, a logic 0 indicates an
inactive (OFF) output.
Status Data
Status data is an 8-bit data value that identifies the slave mod-
ule and indicates the default values set by the analog output
default dipswitch (S2). The MFP reads the identification bits
(four MSB) to verify the slave expander bus communication
integrity and MFP configuration. It reads the default bits (four
LSB) to determine the default states set for the analog outputs
in the event of a
time-out
.
