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Old March 17th, 2006, 08:42 AM   #1
AJZ
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Question AB FLEX IO Limits

What are the limits for module use on a AB 1794 FLEX IO system?

I know that the maximum number of modules is eight and the maximum number of I/O points is 256. Based on this info, I can use eight 32point modules. Is that correct?

Also, is there a limitation to the number of input or output modules used?. For example, can I use six 1794-IB32 modules with two 1794-OB32 modules

Adrian
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Old March 17th, 2006, 02:29 PM   #2
Ken Roach
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Disclaimer; I have not worked directly with the 32-point I/O modules but I am very familiar with the fundamentals of the 1794 platform.

The physical FLEX bus can support eight modules of any type. Analog, Specialty, 8-point, 16-point, or 32-point, it doesn't matter.

1794 FLEX is a 16-bit I/O architecture, so if you have 32-point modules you will have to logically communicate with them differently than with 16-point ones.

The most important consideration is which network adapter you are going to choose. Only the newest adapters for RIO, DeviceNet, ControlNet, and EtherNet/IP support the 32-point I/O modules, and they do so in slightly different ways.

The EtherNet/IP adapter, for example, allows you to make a logical I/O connection directly to the 32-point module, which is less efficient than a "rack optimized" connection but still works. I think the RIO adapter requires block transfers.

Get the release notes for the network adapter you will be using and they will have information on how 32-bit support is implemented in that adapter.

Here's a 32-bit module compatiblity table, taken from the 1794-IB32 installation manual:

Remote I/O
1794-ASB series E or later
1794-ASB2 series D or later

ControlNet
1794-ACN15 series C, firmware revision 4.1 or later
1794-ACNR15 series C, firmware revision 4.1 or later

Ethernet
1794-AENT series A, firmware revision 2.4 or later

PROFIBUS
1794-APB series A, version 1.1 of the GSD file

ControlLogixTM Family RSLogix5000 programming software, version 11 or later
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Old March 17th, 2006, 03:23 PM   #3
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Just want to confirm that Ken is correct.
Limit still 8 modules.
Correct adapter must be used that supports 32 bit mode.
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Old March 17th, 2006, 08:34 PM   #4
AJZ
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Thanks, Ken.

I am working on a new system using DeviceNet as the Network. A CLX L61 is the PLC.

Ken, I noticed that you did not list a DeviceNet module in your list. Does that mean I cannot use the 32point modules?

Adrian
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Old March 18th, 2006, 08:17 AM   #5
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Check these technotes for 32 point modules and 1794-ADN:


P20842 - 1794OB32P, 1794IB32, 32 point Flex I/O module and supported adapters.

Q110737688 - DeviceNet: 1794-ADN f/w 2.002 issue with Autoscan and 1794-IB32 or 1794-OB32P

A63745719 - Configuring 32 point discrete Flex I/O on a 1794-ADN DeviceNet adapter

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Old March 18th, 2006, 09:48 PM   #6
Ken Roach
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Thanks for those, Control_Conn.

Those knowbase articles are more thorough than the installation instructions that I downloaded. See what happens when we let literature majors do engineer's work !

FLEX is a pretty old architecture and I'm grumpy about the way it works on DeviceNet (complex to map and maintain), but it's a good way to get a lot of I/O in a small space, especially when you connect it up on ControlNet or EtherNet/IP.
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