Need help with bit data file.

Can anyone explain to me how does the address scheme for a bit data file works? For example, B3:400 and B3/47 I am using the PLC 3rd edition by Frank D. Petruzella in chp5, p97 par 2 he refers to B3/47 as Word 2, bit 15 I do not understand. Also, can anyone suggest any examples that I can use as a guide. Any help will be appreciated.

EWORD said:

Can anyone explain to me how does the address scheme for a bit data file works? For example, B3:400 and B3/47 I am using the PLC 3rd edition by Frank D. Petruzella in chp5, p97 par 2 he refers to B3/47 as Word 2, bit 15 I do not understand. Also, can anyone suggest any examples that I can use as a guide. Any help will be appreciated.

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The general format is
FILETYPE-FILENUMBER:ELEMENT_NUMBER/BIT_NUMBER

B3 means a bit file, file #3.
N7 means an integer file, #7

B3:400 refers to an entire 16 bit word, it is word #400 in bit file 3. B3:400 is 100% interchangeable with an integer. B3:400/0 would refer to the first bit in that word.

B3/47 is bit number 47 in the bit file. Bit 47 happens to be in the last bit in word 2, so B3/47 and B3:2/15 refer to the same address.

You can address bit file words at the integer level, as in B3:400 or you can address the individual bits in an integer, for example N7:0/15 refers to the last bit in word N7:0. This is something that is handy to remember, because if N7:0/15 is set then the value in N7:0 is negative.

A few programmers don't use bit files but rather use bit access of integers, do instead of using B3:0/0 (same as B3/0) the would use N7:0/0. As far as the PLC is concerned there is no difference between the two methods. RSLogix software however does not recognize the File/Bit shortcut with integer files, so while you can enter B3/47, you cannot enter N7/47 but rather would be requried to use N7:2/15.

Edit to add:
Take a look at this screen shot of the bit file from the programming software. The bits are arranged into 16 bit words, the word number is shown on the left hand side and the bit number is designated in the column heading at the top. Notice that Bit B3/47 is selected. If you look to the left you can see that it is in word 2 and if you look to the top you can see that it is bit 15. If you want to be bothered to do it, start in the top right at word 0, bit 0, and count the bits starting at zero. You will count to 47.