DESCRIPTION AND OPERATION
CONTROL LOGIC
I-E96-309A
2 - 3
CONTROL LOGIC
Function Code (FC) 84 in the master module configuration
accesses the DSM on the slave expander bus. It also allows the
master module to automatically read point (input) data or sta-
tus data from the DSM. This data is output by the buffer cir-
cuits (control logic) to the slave expander bus interface (see
Figure
). The slave address in FC 84 must be the same as
the address set on the slave address dipswitch (S1).
Point Data Byte For MFP/LMM
The DSM transfers two 8-bit bytes of point data at once to the
master module. Each byte corresponds to group A or group B
inputs. Each bit of data represents one input. The bit value
reflects the state of that input, either open (logic 1) or closed
(logic 0). The DSM transfers two 8-bit status bytes at once to
the master. One byte for group A and one byte for group B. The
MFP or LMM reads the status bytes associated with that group
to determine if it will read the data in the point groups set as
inputs or write data to the groups set as outputs.
Status Byte
The status byte ensures module integrity and tells the master if
the data in the 8-bit data byte is from an input group or an
output group. It makes sure slave expander bus communica-
tion and master module configuration are correct. The master
Figure 2-2. I/O Circuit
+5 VDC
+5 VDC
+24 VDC
5.36 K
1.5 K
220 K
10 K
3.52 K
1 2 3
INPUT CIRCUIT
OUTPUT CIRCUIT
TP35714A
