Assembler code

[abelmeg]

Posted on January 01, 2010 at 08:30

Assembler code

[abelmeg]

Posted on May 17, 2011 at 15:06

I'm using the STM8s for my application on motor control and here is the code I am confused about.

ld A,_Average_Zero_Cross_Time

ld XL,A

ld A,_tmp_u8

mul X,A

ldw _tmp_u16,X

ld A,_Average_Zero_Cross_Time + 1

ld XL,A

ld A,_tmp_u8

mul X,A

ld A,XH

clrw X

ld XL,A

addw X,_tmp_u16

ldw _Demag_Time,X

It tries to do: Demag_Time = (Average_Zero_Cross_Time * tmp_u8) >> 8;

Can't I do it by using the code below:

ld A,_Average_Zero_Cross_Time

ld XL,A

ld A,_tmp_u8

mul X,A

ld A,XH

clrw X

ld XL,A

ldw _Demag_Time,X

regards...

[fggnrc]

Posted on May 17, 2011 at 15:06

abelmeg,

if Average_Zero_Cross_Time is a two byte quantity, its product by tmp_u8 (which I suppose is an eight bit quantity) is a three byte quantity.

The most significant byte of this product is:

HIGH_BYTE( HIGH_BYTE(_Average_Zero_Cross_Time) * _tmp_u8)

The middle byte is:

LOW_BYTE( HIGH_BYTE(_Average_Zero_Cross_Time) * _tmp_u8) + HIGH_BYTE( LOW_BYTE(_Average_Zero_Cross_Time) * _tmp_u8)

Finally the least significant byte of this product is:

LOW_BYTE( LOW_BYTE(_Average_Zero_Cross_Time) * _tmp_u8)

So, only your first code is correct.

_tmp_u16 isn't however needed, since it can be replaced with _Demag_Time.

Happy new year!

EtaPhi

[abelmeg]

Posted on May 17, 2011 at 15:06

Dear EtaPhi,

First of all I would like to thank you for your reply, But Average_Zero_Cross_Time is only an 8-bit quantity and the result of multiplication would be in the 16-bit index register X.

Regards..

[abelmeg]

Posted on May 17, 2011 at 15:06

I got it now! I didn't consider the addition(+1) as address.

thank you and have a prosperous new year!