DESCRIPTION
CONTROL LOGIC
WBPEEUI240752A0
2 - 3
Input Circuit Connections
The contact input signals connect to the 30-pin card edge con-
nector (P3), shown in Figure
, using a termination cable
from a termination unit or termination module.
CONTROL LOGIC
Function Code (FC) 84 in the control module configuration
accesses the DSI on the I/O expander bus. It also allows the
control module to automatically read point (input) data or sta-
tus data from the DSI. This data is output by the buffer circuits
(control logic) to the I/O expander bus interface (Fig.
). The I/
O address in FC 84 must be the same as the address set on
address dipswitch (S1).
Point Data Byte
Point data is two 8-bit bytes . 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 0) or
closed (logic 1).
Status Byte
The status byte ensures module integrity. It makes sure I/O
expander bus communication and control module configura-
tion are correct. The control module reads the status byte and
compares it to an expected value. If a mismatch occurs, it flags
the error and marks the point as bad quality.
Figure 2-2. Digital Input Module Circuitry
T00103A
INPUT CIRCUITRY
THRESHOLD AND
FILTERING BLOCK
+5 VDC
+5 VDC
JUMPER
JUMPER
RESISTORS
B
C
B
A
A,D
JUMPER
ISOLATION
VREF
DI–
DI+
1
1
NOTE:
A = MOUNTED ON IMDSI12
B = MOUNTED ON IMDSI14
C = MOUNTED ON IMDSI13
D = MOUNTED ON IMDSI15
A-D
–
+
LED
DIGITAL
INPUT
+5 VDC
VREF
