ControlLogix Structure Bit Word

I am designing a system with a ControlLogix 5555 processor that will communicate to five AB1336E drive on ControlNet through a 1203-CN1 CNet to ScanPort adapter. In the CLX program I want to create a user defined data type that represents my data coming back from and going to the drives. My problem is in the status and command bit words. When you define a BOOL in a structure, Logix5000 immediately reserves a DWORD and fills in consecutive BOOLs in that DWORD until the DWORD is full. The 1203-CN1 and the 1336E send back the command and status words as 16-bit words. So trying to embed a bit structure into the drive data structure will shift all the words after the bit words by one word.
Is there a way to force Logix5000 to use a 16-bit word when defining a structure of BOOLs for a case such as mine?

Thanks,
Keith

Nope. You can either use the BOOL data type and ignore the upper 16 bits or just use an INT and access it at the bit level. That is what I do for accessing over DeviceNet or ControlNet.

Logix 5000 will "jump ahead" after a BOOL to the next 32-bit boundary in a UDT if the next element is 32 bits or larger, but not if the BOOLs are followed by a SINT or INT.

When I use 16-bit SCANport devices on DeviceNet or ControlNet, I use several BOOL (less than 16) elements followed by an INT element for the speed reference/ feedback. This makes a UDT that is only 4 bytes (2 Words) long and fits the SCANport image perfectly.

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I agree with Ken, define a data type and use it. There is a knowledge base note on the AB site that describes their use.

Thanks guys.
I was trying to get too cute. I was making a second UDT that was a bit layout for the command and status words. In your example the start bit is dereferenced as Drive.Start. I was trying to do something like Drive.Command.Start with Command being a separate UDT that contained only BOOLs. In that case the UDT Command comes out as 4 bytes and if I put that in my Drive UDT the data would get shifted.

Thanks again.
Keith

Oh ! I hadn't thought of making a compound UDT for that. Yes, I can see how that would expand to 4 bytes and screw up your intended structure.

Good luck with the IMPACT drive project !