PLC5 Indirect addressing

Hi Everybody,

I never have used indirect addressing in AB PLC5, but used it in SLC5/04. Today I found out PLC5 don't allow bit level indirect address, it shows "incorrect bit address" while tried to assemble the rung. But I have used the similar code in SLC, no problem at all.

What I was trying to do is this, register the parts in a word for the purpose of comparison with another word. By the way it is a PLC 5/30

B3:0             N7:0

-][---------------(L)--

 0             C5:0.ACC

Anybody come across this, any clue?

Thank You

I forgot about that little gotcha. It's been a while since I've done much PLC5 stuff.
What I would do is use a bit word as an intermediate placeholder. You can inderect address at the bit level with B words if you use bit level entry. To work out exactly right you will need to use B?:0 as the scratchpad word.

      B3:0                    B13 

------] [---------------------(L)--

       0                   [C5:0.ACC]      



                      --MOV------

---------------------|     B13:0 |--

                     |     N7:0  |

                      ----------- 

Keith

Thank you Keith for the suggestion.

I'll try it out. If I understant correctly your method will only allow Word 0 as a target.

But I think somehow SLC is far superior compared to PLC5 when come to indirect addressing.


Thank You

If I understant correctly your method will only allow Word 0 as a target.

Click to expand...

NO.

There are two methods of addressing binary (B) files:

• B<file>:<word>/<bit>
• B<file>/<bit>

Use the 2nd method to use indirection.

B3/20 is equivalent to B3:1/4

Make sure the counter's accumulator is valid for the size of the binary file you are referencing.

Thankyou Gerry for the information. I understand it now.

Attached image is the illustration of the ladder for indirect addressing in PLC5. An image of data table B3 is also included.

Take note this was created only for "illustration". In actual I didn't used it this way.

Hope, it is of use to somebody, someday.

Thank You