Instruction Manual

Chapter
1
1-1
Introducing Block I/O
In this chapter, you will learn what analog block I/O is, its features, and
how it functions.
Block I/O consists of small, self-contained remote I/O devices complete
with power supply, programmable controller interface, input/output
connections and signal conditioning circuitry. Table 1.A is a list of block
I/O modules covered in this publication.
Table 1.A
Types
of Block I/O
Catalog Number Power Supply Voltage Inputs Outputs Description
1791N4V2 120V ac 4 2 analog - 4 input, 2 voltage output
1791N4C2 120V ac 4 2 analog - 4 input, 2 current output
1791NDV 24V dc 4 2 analog - 4 input, 2 voltage output
1791NDC 24V dc 4 2 analog - 4 input, 2 current output
The analog blocks are compatible with PLC-2

, PLC-3

, PLC-5/250

and
PLC-5

family programmable controllers, and the SLC

5/02 (or greater)
modular controllers. Refer to the table below for information on using
block I/O with various Allen-Bradley programmable controllers.
If You are Using: You must use:
PLC2 family programmable controller
1771SN subI/O scanner or
1772SD and SD2 remote I/O scanners
PLC3 family programmable controller
PLC5 family programmable controller
Block attaches directly to controller
PLC5/250 programmable controller
y
SLC 500 programmable controller 1747SN remote I/O scanner
The analog blocks communicate via block transfer or discrete transfer with
any Allen-Bradley programmable controller that connects to the remote
I/O network. The analog blocks communicate with SLC family controllers
using discrete transfer.
Each analog block has four independent inputs, which can be configured as
either all voltage inputs or all current inputs. The block contains a 24V dc
current limited voltage source for accommodating loop-powered current
transducer inputs.
Chapter Objectives
General Description