1785-L20B

Technical specifications

Manufacturer

Allen-Bradley

Manufacturer part no.

1785-L20B

Type

PLC-5 processor

Application

PLC controller

Used with

1771 I/O chassis (leftmost slot)

Processor

PLC-5/20

Maximum user memory (words)

16K

Total I/O, maximum

512 any mix or 512 in + 512 out (complement)

Channels

1 DH+; 1 DH+/remote I/O

I/O chassis, maximum total

13

Remote I/O chassis, maximum

12

Power dissipation, maximum

12W

Backplane current load

2.3A

Operating temperature

0...60 °C (32...140 °F)

Storage temperature

-40...85 °C (-40...185 °F)

Relative humidity

5...95% noncondensing

Vibration

2 g @ 10...500 Hz

Shock

Operating 30 g; non-operating 50 g

Enclosure type rating

None (open style)

Time-of-day clock/calendar

Maximum variation at 60 °C: ±5 min per month; typical at 20 °C: ±20 s per month

I/O modules

Bulletin 1771 I/O, 1794 I/O, 1746 I/O, and 1791 I/O, including 8-, 16-, 32-pt and intelligent modules

Hardware addressing

2-slot, 1-slot or 1/2-slot

Location

1771-A1B, -A2B, -A3B, -A3B1, -A4B chassis; leftmost slot

Replacement battery

Allen-Bradley 1770-XYC

Available cartridges

1785-RC Relay Cartridge

Memory modules

1785-ME32, 1785-ME64, 1785-M100

Communication

Serial; DH+; DH using 1785-KA; remote I/O

Isolation voltage

Communication ports tested to 500V for 60 seconds

Weight

3 lbs, 3 oz (1.45 kg)

Technical documents (1)

• Rockwell Automation publication 1785-IN062 (specifications)

Key features

• Two channels: 1 DH+ and 1 DH+/remote I/O
• Up to 12 remote I/O chassis supported
• Works with Bulletin 1771, 1794, 1746 and 1791 I/O
• Fits leftmost slot of listed 1771 chassis
• Open style enclosure, operates from 0 to 60 °C

About the Allen-Bradley 1785-L20B

The Allen-Bradley 1785-L20B is a PLC-5/20 processor, described by Rockwell Automation as a PLC-5 Processor. Rockwell publication 1785-IN062 lists maximum user memory of 16K words, total I/O of 512 any mix or 512 in plus 512 out (complement), and up to 13 I/O chassis in total, including up to 12 remote I/O chassis. Backplane current load is 2.3A and maximum power dissipation is 12W. Rockwell's Product Lifecycle Search shows it as discontinued on 31 December 2014, with the replacement category Engineering Replacement.

What is the 1785-L20B used for?

The 1785-L20B holds and executes the user program in a PLC-5 system, mounted in the leftmost slot of a 1771-A1B, -A2B, -A3B, -A3B1 or -A4B chassis. It works with Bulletin 1771, 1794, 1746 and 1791 I/O, including 8-, 16-, 32-pt and intelligent modules, and communicates by serial, DH+, DH using 1785-KA, and remote I/O. Rockwell lists memory modules 1785-ME32, 1785-ME64 and 1785-M100, the 1785-RC Relay Cartridge and replacement battery 1770-XYC for use with it.

Lifecycle and successor

Discontinued.

Before you order

What to photograph or confirm so the right unit is quoted.

Check that the label reads catalog number 1785-L20B, and note the series letter and firmware revision printed on it. Send us a photo of the label if you would like us to confirm the details before ordering.