Pointer Format

manmeetvirdi · Dec 18, 2009

OK if code is ...

LAR1 P#M 0.0
L N
SLD Y
+AR1

Now AR1 is pointing to byte Nx2^(Y-3) of M address area.
Maximum possible value of Y is 14, and the minimum value is 3.Because if less then 3 then it comes to bit area of the pointer.
Question is why the maximum value of Y is 14 (when N=1), it should be 15.

PeterW · Dec 18, 2009

Pointer address is a DWORD, 32 bits.

The DWORD is made up of

aaaa aaaa xxxx xwww wwww wwww wbbb

a= memory area
x= unused
w= word address
b= bit address

manmeetvirdi · Dec 18, 2009

Hello PeterW

Actually was concerned with Byte 4 and 5 of the pointer .

If N=1 and we do SLD14 then bit reaches up to 14th bit of Word (and points to 2048th byte) and one bit is vacant still.May the attached picture explains the best

PeterW · Dec 18, 2009

PeterW said:
Pointer address is a DWORD, 32 bits.

The DWORD is made up of

aaaa aaaa xxxx xwww wwww wwww wbbb

a= memory area
x= unused
w= word address
b= bit address

Miscounted the number of bits I put in

aaaa aaaa xxxx xwww wwww wwww wwww wbbb

is the actual.

Why is the maximum value 14?

The pointer is a double word (32 bits) not 16, you can place a 1 then SLD3 to get the least bit of the word address or SLD18 to the highest bit of the word address.

So I'm unsure why you say 14 is the max.

18 is the max, the pointer is 32 bits not 16.

Of course you are limited by the size of the start number.

L D[AR2P#0.0] · Dec 18, 2009

The +AR1 instruction is the limitation - see help as below

Description

+AR1 (add to AR1) adds an offset specified either in the statement or in ACCU 1-L to the contents of AR1. The integer (16 bit) is initially expanded to 24 bits with its correct sign and then added to the least significant 24 bits of AR1 (part of the relative address in AR1). The part of the area ID in AR1 (bits 24, 25, and 26) remains unchanged. The instruction is executed without regard to, and without affecting, the status bits.

+AR1: The integer (16 bit) to be added to the contents of AR1 is specified by the value in ACCU 1-L. Values from -32768 to +32767 are permissible.

+AR1 <P#Byte.Bit>: The offset to be added is specified by the <P#Byte.Bit> address.

manmeetvirdi · Dec 19, 2009

So I'm unsure why you say 14 is the max.

18 is the max, the pointer is 32 bits not 16.

Ok PeterW I missed showing why I was saying 14 is the Max.
As per the picture with SLD15 it should point to 4096 but in actuality its different !!

LD read it, but dint got it......!!

L D[AR2P#0.0] · Dec 19, 2009

When you add to AR1 using the +AR1 instruction, the lower 16 bits of accu 1 are treated as a signed number. The maximum positive number you can represent in 16 bits is 7FFF = 32767 = P#4095.7

The +AR1 instruction allows you to specify negative numbers for the addition hence allowing you to index backwards through a table if you want to.

If you want to add a positive number greater than 7FFF = 32767 = P#4095.7 to AR1, you have to use the +D instruction. See example code below:

manmeetvirdi · Dec 19, 2009

Wow LD amazing.....
Got the point......

You were in the Step 7 development team right??

Pointer Format

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