1734-ow4/c

Just curious about something. This card is a 4 point relay output card so it only has 4 outputs. But in the Controller tags when you look at that card it shows 8 bits. See picture

Prayder said:

Just curious about something. This card is a 4 point relay output card so it only has 4 outputs. But in the Controller tags when you look at that card it shows 8 bits. See picture

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That is because it uses the 8-point "Module-Defined Data-Type".

This happens a lot for many modules, as it saves having to have unique data-types for all the modules.

You simply ignore the upper 4 channels.

I figure Rockwell had a choice between using four BOOL elements and using a SINT with four unused points, and chose the latter for consistency.

Consider the 1734-IB4D modules I'm using with NO/NC complementary output prox switches. The first four bits give me the status of the four actual input points, and the second four bits give me open-wire/short-circuit status for those input points.

You will find that sort of thing elsewhere in the ControlLogix world; some 16-point input modules have a 32-point data tag, even though they don't use it. It's just easier for the Studio 5000 developers, the firmware developers, and us users to have consistent datatypes for modules that are members of the same family.