General Information Technote: 1794-ASB Series E Remote I/O Adapter Module: New Installation and Replacement Module Guidelines

General Information

G58255798 - 1794-ASB Series E Remote I/O Adapter Module: New Installation and Replacement Module Guidelines

Last Modified: 06/14/2004

General Category:	s	Programmable Controllers - I/O
Product(s):		Flex (1794)
Catalog #:		1794ASB
Series / Revision:
Subject (Keyphrases):		compatibility, configuration, instructions
Summary of Technote Information:

1794-ASB Series E Remote I/O Adapter Module: New Installation and Replacement Module Guidelines

A-B Flex I/O Remote I/O Adapter Modules (1794-ASB)

History

Since its introduction in May, 1994, the 1794-ASB Remote I/O Adapter (-ASB) has had a number of enhancements. The revision level on the product ID label changes whenever a small, directly downward compatible product change is made. However, when a product change to form, fit or function occurs, the Series designator of the catalog number is modified. Our current shipments of the 1794–ASB are at Series E.

One of the reasons for the change to the Series E designation was that the –ASB was now able to support 32-point FLEX I/O modules where previous series modules did not have that capability. In order to designate Autobaud/32-point mode operation in the Series E 1794–ASB adapter, one of the redundant switch settings for 230kbaud operation was redefined. See the table below for switch definitions for the current and prior series modules.

Table: 1794-ASB Switch Selection

Switch 2 Position 3	Switch 2 Position 4	Function prior to Series E	Function in Series E
ON	ON	57.6 KB	57.6 KB
ON	OFF	115.2 KB	115.2 KB
OFF	ON	230.4 KB	230.4 KB
OFF	OFF	230.4 KB	Autobaud/32-point mode

Implications of undesired selection of "Autobaud/32-point" mode selection with Series E 1794-ASB

1. I/O image bits will be remapped. This is undesirable and could affect control operations. Do NOT run the system! If your rack is configured for the standard 16-point rack size and you attempt to operate in 32-point mode, input data will be mapped to the incorrect input image bits and output data table image bits will be sent to the wrong output modules.

2. The –ASB adapter may or may not indicate a rack fault depending upon whether or not an I/O rack overlap condition occurs and the order in which adapters are powered up on the remote I/O network.

IN ANY EVENT: Do NOT run the system with switch 2, positions 3 and 4 both in the OFF position unless you specifically have that specific FLEX I/O rail designed for 32-point operation.

If the intent is simply to replace a Series C or Series D 1794–ASB adapter that had switch 2, positions 3 and 4 in the OFF, with a Series E 1794-ASB then:

-Set switch 2, position 3 OFF
-Set switch 2, position 4 ON

This selection will allow the Series E 1794-ASB to operate at 230kbaud in the standard 16-point mode.

For more information see Remote I/O User Manual Publication #1794-UM009C-EN-P (March 2003).

Module Nametags

The following modified switch setting nametag and new nametag have been added to the module for Autobaud/32 point mode.

SW2 1 HOLD LAST STATE
SW2 2 PROC RESTART LOCKOUT
SW2 3-4 BAUD RATE/32 POINT MODE
SW2 5 MODE 1
SW2 6 RACK FAULT SELECT
SW2 7 HOLD INPUTS
SW2 8 MODE 0

SW 1 1 MODE 2
SW 1 2-6 I/O RACK NUMBER
SW 1 7-8 FIRST I/O GROUP

NOTE: SW2 Pos3-4

NEW DEFINITION

OFF OFF 32 PT MODE
OFF ON 230K BAUD

Guidelines for Replacement of the A-B FLEX I/O Remote I/O Adapter Module, Catalog No. 1794-ASB

When replacing a 1794-ASB adapter module, it is important that the following guidelines for DIP SWITCH settings are followed:

1. Remove power from the adapter. Swap units.

2. If the "old" module is a 1794-ASB Series A, B, C, or D and had: Switch 2, Positions 3 and 4 set to OFF, OFF (or 0, 0)

3. THEN set the "new" module: Switch 2, Position 3 to OFF (or 0 ); and Position 4 to ON (or 1)

4. Apply power to the "new" adapter.

Guidelines for Implementing 32 Point Addressing

1. When implementing any 32 point Addressing Mode, we are limited to a starting I/O group of (Zero) (S1-7,S1-8) Must both be ON

2. When implementing any 32 point Addressing Mode, the Autobaud feature of the module is enabled. This permits RIO communication at any baud rate without user selection. The baud rate still has to be set on Switch 2 when the 32 point Addressing Mode is NOT used. Autobaud is only supported in 32 point Addressing Mode.

Notes:

Series E, Firmware Revision C modules had a problem with the Autobaud feature when communication baud rates of either 57.6KB or 115.2 KB were selected.
See KnowledgeBase Doc ID No. P42978616 for details.

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