A2SH

[Guest Guest_Dejan]

Hi, Can anybody tell me the difference between direct I/O and refresh I/O? Thanks, Dejan

[Crossbow]

Direct I/O is read from the real world devices exactly when you use it in the program. Refresh I/O uses the I/O table built at the beginning of the PLC scan. The way your PLC processes, first it reads all it's I/O, then it processoes the program updating the memory table of the I/O, then it updates the real I/O at the end of the scan. Then it starts over at the top. A direct I/O will check the actual input status at the exact point in the program where used. Keep in mind using too many of the direct type will slow down the CPU scan time.

[Colin Carpenter]

What is the default mode for Mitsubishi PLCs? Must admit that in 20 years of programming these things, I've never *truly* got my head around when one way is preferable to another. Anybody got any preferences?

[andybr]

Direct used to be the default mode on older Mitsubishi processors but I do not think it is even available on the current models. I always preferred to use refresh as I feel that this makes the system more predictable.

[maccxim]

Yes Direct mode was used long time ago, for example when there was problems of fast input events and cpu was not so high speed. So, combination of diretc mode and repeating of input contacts in a program, it was possible to solve input high speed problems. Now, with actually cpu models don't need about this funtion, just to use fast scan-time of cpu or if you need you can use special instructions. bye Max