Can someone help to understand how pointers work?

Hi guys,

I´m trying to understand how pointers work. So far I have a good idea but I have run on part of code in my Company and I have no idea what it does.

Here is the code:

L     P##DataBusWrite
LAR1
L     W#16#10
T     LB [AR1,P#0.0]
L     W#16#2
T     LB [AR1,P#1.0]
L     #LengthDataBusWrite
T     LW [AR1,P#2.0]
L     240
T     LW [AR1,P#4.0]
L     0
SLD   3
L     B#16#84
SLD   24
OD
T     LD [AR1,P#6.0]

Now, I understand everything till line 11 and beyond.

Why load 0 and then rotating it for 3 bits to left? Makes no sense.

And on line 13, L B#16#84 is code for Memory area of DB. Why shiffting it to left for 24 bits? And then using logic OR function?

------------------------------------------------------------------------------------------
Split from Format of the parameter Type POINTER.

Hello Dr.Rock.

You can convert an Int data type to pointer data type by just shifting the Int 3 places to the left. Remember that pointer data type uses 3 bits for bit address .0 to .7.

Why they shift 24 places the 84H, I'm not sure.

I'll think about it a little more and let you know my thoughts.

Hope I can help.

Regards.

DR. Rock.

What the code is doing is creating an ANY pointer.

the instruction SLD 24 is converting the 84H to pointer data type and its moving it to the start of byte 6 when the OD instruction gets executed.

Remember that ANY pointer is 10 bytes long and byte 6 corresponds to Memory area, that is why they move the 84 24 bits to the left.

When OD executes, give as a result:

on byte 6: 84

bytes 7,8 and 9 contain the byte address.

I hope I was clear and that this help you.

Hi Rescobedo,

Thank you for the explanation.

It makes sense now.