When to use b3 and n7 in Logix500

I am converting some programs from GE 90 30 to AB Logix 500 and have a wonder about the use of the B3's and N7's. The AB programs that I have used as reference were done by an integrator in the past who used mostly N7 for bits ie. N7:10/3 on contacts and coils. There are some B3 but not many. Another integrator that I talked to said that as a matter of standard one should use B3 for bits and N7 for integer values. I know that both work just fine for bits but is there a preferred or more standard method? One thing that the N7 integrator did was utilize masking, could that be why he used N7 more?
Thanks.

Steve

In answer to both questions, YES. As pratice I have tried to use the
"B" for common relay logic coils and contacts. The reason the N7 integerator chose to use the "N" could be the type of operator interface is connected, if any. Some 3rd party OI's will only allow one format for data transfer. Or this data could be put in some type of communication format and passed to another PLC using a MSG or the Block Transfer. I have been around this for some 20 years and I have seen all kinds of programming. What ever path you take DOCUMENT each one address you use. Logix has a 5 x 20 char. description for each address. Also included are rung descriptions and address tags.

I hope this helps.

AJW

In the PLC5, and most likely the SLC500, using B3 addresses for bit instructions uses less memory.
In the 5, it took 2 words of program memory to store the address of a B3 bit (up to a point), vs. 3 words for bits in higher numbered files. There was a point in the B3 file where 3 words would start to be required. That point varied depending on the size of the I/O image tables and status area.

To expand a little on the previous posts - don't limit yourself to N7 and B3. It can help a lot, organizationally, to group related functions in unique files.

Say the processor controls three lines. Group all the bits dealing directly with line #1 in, say, B11; those for line #2 in B12, etc. Continuing, you could put the integers for line one in N21, and so on.

Doing this will use a little more memory but, the benefit in understandability is worth it - IMO.

.02