Introducing Block I/O
Chapter 1
1-4
Discrete transfer (Figure 1.3) is intended to be used with controllers which
do not have block transfer capability. However, discrete transfer can be
used with any PLC family controller. When using discrete transfer, the
block looks like a 1/2 I/O rack to the controller (four words of input image
table memory and four words of output image table memory). Note that
certain alarms and user scaling features are not available when using
discrete transfer.
Figure 1.3
Block I/O Connection in an SLC System using discrete transfer
Blocks are daisychained to
a scanner
1747SN Remote I/O
Scanner Module
10828I
= 1 I/O Rack
Block I/O each block
is 1/2 I/O rack
+
1/2
1/2
A simplified schematic of the input circuit of one input channel is
shown below.
RET in0
Simplified Schematic
1
1
inV0
inI0
GND in0
A/D
20M
Ω
249
Ω
20M
Ω
Analog Multiplexer
Instrumentation
Amplifier
Channel 0
Channel 1
Channel 2
Channel 3
Channel 0 Input
+
-
12501-I
Analog Input
Common
ATTENTION:
The 249 ohm
input current shunt is rated at
0.25 Watts. Do not exceed this
power rating or apply more
than 6V across the resistor
Analog Input
Common
Inputs have selectable input ranges as shown below.
Application
Input Range Resolution
voltage
+10V
14 Bits
voltage or current
+5V
14 Bits
voltage
0 to 10V
14 Bits
voltage or current
0 to 5V
14 Bits
Inputs
