CodeWarrior for MCUのトピックBRSET - assembly listing

BRSET - assembly listing

leesp — Wed, 24 Nov 2010 17:40:42 GMT

Hi,

I am using CodeWarrior for MC9S08. I am trying to understand the assembly listing in the True-Time Simulator & Real-Time Debugger. The first line of the listing is

0000 000000 BRSET 0,0x00, *+3 ;abs = 0x0003

but from what I understand from the instruction set, the source and object code for BRSET is:

Source

BRSET n, opr8a, rel

Object

00 dd rr (assuming we are dealing with b0)

Therefore the object code should be 000003.

Why is it 000000 instead?

Re: BRSET - assembly listing

kef — Wed, 24 Nov 2010 17:49:03 GMT

rel is relative to the first byte of next instruction. * is first byte of current instruction. So *+3 and opcode is correct.

Re: BRSET - assembly listing

leesp — Wed, 24 Nov 2010 18:17:08 GMT

Hi Kef,

Pardon me I still don't understand. Am I right that

BRSET 0,0x00, *+3 means:

Branch if bit 0 in memory location 0x00 is set; the branch-to location is +3 bytes from the next instruction?

Then according to:

Source

BRSET n, opr8a, rel

Object

00 dd rr , n = 00, opra8a = 0x00, rel = +3, the opcode should be 000003 right?

Please help to answer. Thanks..

Re: BRSET - assembly listing

kef — Wed, 24 Nov 2010 18:31:23 GMT

BRSET 0,0x00, *+3

Is the same like

L1: BRSET 0,0x00,L2

L2:

* is quivalent to L1

rel is calculated relative to L2. rel=0 means branch from L2 to L2+rel = L2+0 = L2

Re: BRSET - assembly listing

leesp — Wed, 24 Nov 2010 18:41:14 GMT

Ok Kef, thanks a lot I understand now.

I didn't know " * " means the current program counter value. I think the MC9s08 user manual assume a newbie like me understand this!

Where can I find out more fundamental things like this (since the uC manual does not provide this information)?

Re: BRSET - assembly listing

kef — Wed, 24 Nov 2010 19:01:49 GMT

* should be mentioned in Codewarrior assembler manual. Disassembler just uses same notation.