Difference between W and D registers on Mitsubishi?

Bobbias · Nov 30, 2011

I'm working on a job right now that requires me to work with a Mitsubishi Q series PLC. I've never worked with one before and I've been wondering what the difference between a D Register and a W register is... I haven't been able to find any documentation that actually describes the purpose of these memory locations...

Mark- · Nov 30, 2011

Hi,

From the manual:

Data registers are memory devices which store numeric data (-32768 to 32767, or 0000H to FFFFH).

A link register is the CPU module memory used to refresh the CPU module with data from the link registers (LW) of intelligent function modules including MELSECNET/H network module.

Bobbias · Nov 30, 2011

So if there are no intelligent function modules using them, the W registers are functionlly the same as D registers?

Edit: Which manual, by the way, Mitsubishi has so many of them it's hard to know which manual I should be looking for things in.

Mark- · Nov 30, 2011

Hello,

Maybe.

I have not used all the instructions.

Some instructions might exist that do not access the link registers. Most places in the manual when D registers are used it appears that L registers can also be used.

Are you running out of D registers?

Bobbias · Nov 30, 2011

No, I was just curious. I'm working with an AJ61QBT11 CC-Link module (to connect to an FR-E700) and I heard from a colleague that if we were going to use the remote registers we were to use them on D registers, not W registers. He said that our customer used W registers for something else.

We won't need to use the remote registers for this module anyway, so I doubt it makes a difference.

Thanks for the quick replies.

Mark- · Nov 30, 2011

Hi,

Yeah the manuals make you into a great sleuth!

This was the QCPU User's Manual ( SH(NA)-080484ENG-M ), section: 10.2.13

Chris Taylor · Nov 30, 2011

Bobbias

I don't think functionally there is any difference between a “W” and “D”, the addressing is different

A “W” is in HEX so 01,02….0E,0F, 10,11 ETC
A “D” in Decimal so 01,02…..09,10,11 ETC

“W” is called a “Link register”
“D” is called a “Data register”

It’s the same with the bits “B” & “M”

“B” is a “Link relay”
“M” is an “Internal relay”

When I’ve use GX developer or GX IEC Developer or its predecessors, I always used “D” for internal registers and “W” for anything for HMI’s SCADA or anything on a network, with multiple PLCs I set myself the “W” (and “B”) range across the PLCs and it makes for easy non-deterministic data exchange

Chris

muttleydoo · Dec 4, 2011

W registers are used with the AJ61QBT11 CC-link module and others. Say if you are using a CC-link connected AD module the values would be read back to the PLC CPU using W registers. This is true also when using multiple CPU's like the Q series servo CPU, all data is exchanged using these registers.

Hope this helps

J Lazo · Feb 23, 2024

Chris Taylor said:
Bobbias

I don't think functionally there is any difference between a “W” and “D”, the addressing is different

A “W” is in HEX so 01,02….0E,0F, 10,11 ETC
A “D” in Decimal so 01,02…..09,10,11 ETC

“W” is called a “Link register”
“D” is called a “Data register”

It’s the same with the bits “B” & “M”

“B” is a “Link relay”
“M” is an “Internal relay”

When I’ve use GX developer or GX IEC Developer or its predecessors, I always used “D” for internal registers and “W” for anything for HMI’s SCADA or anything on a network, with multiple PLCs I set myself the “W” (and “B”) range across the PLCs and it makes for easy non-deterministic data exchange

Chris

Thanks for the clear answer!

parky · Feb 23, 2024

W registers are not retentive unlike D registers (when the range is set in the PLC Parameters) for example you can set the D register latch (retentive) range to say D100-D400, W registers are generally used for special cards like NETH for data transfer between PLC's, there are also R registers these are file registers & can be configured as a file stored either in Ram or on a memory card, these are retentive.

Difference between W and D registers on Mitsubishi?

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