About word device D

[ConTexas 0]

Hi, loocking for the better way to program Mitsubishi PLC Q01, I like the D device because I can use the single bit (D0.0....D0.F) like others PLC (Siemens M0.0...M0.7) or Omron (HR0.0...HR0.15) or Allen Bradley SLC500 (B3/0...B3/15), for example. Also, I can move an entire value in a D device with a MOV instruction. I know that D device isn't latched, like M device. But now I say: why M device exists? Is it more powerful than D for something? I ask because this is the first time I program Mitsubishi, and I don't want, when program finished, change all my "D" whith "M". Thanks. Edited 8 May 2005 by ConTexas

[mjrx 1]

Data can be moved into a bit device in groups of 4. -[ MOV D1 K4M0 ]- would move the contents of 16 bit reg. D1 into M0..M15 Also the D device can be latched or unlatched depending on how you set it up in PLC paramater -> I/O Assignment. The M device is not latched, but the L device is. One example I can think of when you have to use 'M' bit instead of 'Dx.x' is with indexed addressing. You cant do "D1.Z0" or "DZ0.6", but can do "M1Z0". Edited 9 May 2005 by mjrx

[panic mode 246]

there is another good reason. each M bit can be individually comented. i wish I could do that with bits in a D registers

[ConTexas 0]

Hi Friends, thanks for reply. Ok for indexing and comment capability.

[Crossbow 294]

With the FX series and older A series Mitsubishi PLCs, you can't address a bit within a D register. Both have a place in the PLC code. But what you say about D not being latched is slightly incorrect. There are areas of memory you can configure to be battery backed. You can configure a range of D registers to be battery backed and therefore latched.