DESCRIPTION AND OPERATION
MODULE BLOCK DIAGRAM
2 - 2
I-E96-303A
®
This compensates for supply voltage variation and unknown
load impedance. All outputs automatically go to 0 percent (1
VDC or 4 mA) at start-up.
Output mode is selectable for each output channel: current (4
to 20 mA) or voltage (1 to 5 VDC). Switches S2 through S15
select the mode for channels 1 through 14 respectively. Refer
to
Section 3
for switch settings. A current limiter in each out-
put circuit provides short circuit protection. For a short condi-
tion, it limits the output current to 50 mA.
Control Logic
The module memory block is a Dual Port RAM (DPRAM) that
acts as a buffer between the MFP and the analog output chan-
nels. An MFP writes output and default values to the DPRAM
for each of the output channels through the slave expander
bus interface. Two sided (dual port) operation allows the MFP
module and ASO circuits to access the DPRAM simulta-
neously. The MFP is given priority when it and the ASO
attempt to access the same memory location.
Programmable Array Logic (PAL) circuits in the control logic
block provide module control for both normal and default oper-
ation. These circuits cycle through the DPRAM, write output
data (analog count) to the D/A converter and select the S/H
circuits. They also monitor the bus fault (
time-out
) signal to
Figure 2-2. Analog Output Circuit
–15 V
TP27146A
FROM SAMPLE/
HOLD CIRCUITS
FIELD
OUTPUT
FEEDBACK
–
+
+24 V
+15 V
–15 V
–
+
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