Hello,

can you share info where you read this? I'm very curious for reading about that. Thnx.

Swagato

We know that the length of the address register is 32 bits whereas the length of DB pointer is 48 bits. Then how DB pointer is saved in an address register.  

That's simple. It is never saved there.

When talking about POINTER parameter, it is 6 bytes long area of memory with some defined interpretation.

Byte 0-1 - DB number if memory area is DB or DI, else 0.

Byte 2 - memory area.

Bytes 3-5 - p#byte.bit address.

And bytes 2-5 are what can be loaded directly to ARx. In case memory area is DB or DI it is up to the coder to ensure that respectively DB or DI is loaded with the DB number defined by bytes 0-1.

For the latter OPN DB/DI can be used.

fritz

Hi Swagato

you are correct that a Pointer is 6 Bytes (48Bits) and Address Registers are 4 Bytes (32 Bits) long.

Pointer format is actually a subset of the ANY Pointer format (which is 10 Bytes/80 Bits long) and the attached has both side by side (taken from Step 7 inbuilt help).

To answer your question "Then how DB pointer is saved in an address register?":

It isn't and just like with ANY Pointers you grab the DB number information separately from the  Pointer to be able to open the DB explicitly and load AR 1 (or 2) with the remaining 4 Bytes (memory area and Byte.Bit address) and proceed from there.

 It isn't and just like with ANY Pointers you grab the DB number information separately from the  Pointer to be able to open the DB explicitly and load AR 1 (or 2) with the remaining 4 Bytes (memory area and Byte.Bit address) and proceed from there. 

Then how

L W[AR1, P#0.0]

the above statement give us the DB number if the DB pointer is loaded in AR1?

From the statement it is seen that the DB number is coming out from abword of AR1

Then how

L W[AR1, P#0.0]

the above statement give us the DB number if the DB pointer is loaded in AR1?

From the statement it is seen that the DB number is coming out from a word of AR1

Swagato

Then how

L W[AR1, P#0.0]

the above statement give us the DB number if the DB pointer is loaded in AR1?

From the statement it is seen that the DB number is coming out from a word of AR1

 

 This statement does not load a part of an AR1, but some other memory pointed to by AR1.

Volume%201%20describes%20Memory%20Indirect%20Addressing.pdf

Volume%202%20describes%20Register%20Indirect%20Addressing.pdf

Volume%203%20describes%20the%20use%20of%20DB%20Pointers%20and%20ANY%20Pointers.pdf

Download these 3 pdfs. I failed to send it by attachment.  

Swagato,

DB pointer for example, p#Db20.dbx24.0, you cannot load directly to address register like 

L p#db20.dbx24.0

LAR1

This will not work.

You can only apply it to a block parameter of type POINTER in order to point to a data address. Step 7 uses this pointer type internally for transferring actual information contained in the parameter like db number and area pointer in this particular case.

For example,

x is declared in a function as an input parameter of POINTER type and this parameter is assigned with db20.dbx24.0 at the calling point to call the function.

Now, the following codes (for example) in the function will give you actual information as follows:

l p##x

LAR1 // the content in AR1 is not the area pointer (last 4 bytes of the POINTER structure) we are interested for. It is related with temporary local data (V) of the calling block (from where this very function is called)

L W[AR1, p#0.0] // this will load accumulator with db number (byte 0 and byte 1 of POINTER structure), here it will be 20

you can continue retrieving byte by byte like

L B[AR1, p#2.0] // this will give you area type (3rd byte of the POINTER structure), here it will be 84h

L B[AR1, p#3.0 // this will give you 4th byte and can easily be interpreted from the structure and data, here it will be 00h

L B[AR1, p#4.0] // this will give you 5th byte, here it will be 00h

L B[AR1, p#5.0] // this will give you 6th byte, the last byte of the structure of POINTER, here it will be 0Ch

But we are mostly interested with the area pointer contained in 3rd, 4th, 5th and 6th bytes as a whole in the structure and mostly usable as well.

So, we can retrieve a double word at a time like

L D[AR1, p#2.0] // area pointer, here the value will be 1000 0100 _0000 0000_0000 0000_1100 0000 in binary (byte order left-most is 3rd and right-most is 6th) or 84 00 00 C0 in hex

At user level, this interpretation can be taken in mind logically. More than this can, of course, be possible from experts.

It may help

Swagato

Volume%201%20describes%20Memory%20Indirect%20Addressing.pdf

Volume%202%20describes%20Register%20Indirect%20Addressing.pdf

Volume%203%20describes%20the%20use%20of%20DB%20Pointers%20and%20ANY%20Pointers.pdf

Download these 3 pdfs. I failed to send it by attachment.  

I couldn't find them, but if the pdfs describe what you presented here, throw them to the bin.