Re: A83: To the z80 wizards...


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Re: A83: To the z80 wizards...




In a message dated 99-05-31 16:09:38 EDT, you write:

> While going through another list of opcodes, there were several opcodes 
> noted 
>  as previously undocumented.  I was just wondering if any of you know what 
> any 
>  of the following mean:
>    SLL  r    ;commands exist for all registers
>    INC IXH  ;besides inc, there is also dec, and it can be loaded into 
other 
>  regs.
>    INC IXL   ; and have other regs. loaded into it. Where did these new 
regs. 
> 
>  come from?
>  There are some other wierd commands as well, but for the actual site, 
visit:
>  http://www.geocities.com/SiliconValley/Peaks/3938/z80sean.txt
>  Any given help will be appreciated.
>  
>  Ted21

IXH and IXL are the high and low bytes of the IX 16-Bit Register. IXL is the 
LSB and IXH is the MSB, and they can be used like any other 8-Bit register 
(except for the special use of the accumulator in some cases) but there are 
commands like "sub IXL", "inc IXh", and "xor IXH" to use, you just have to 
have the right update of the opcodes table for TASM to use them.  I'm not 
sure if they are already included, i think they were only recently released 
like last fall, and the new .tab file is somewhere on ticalc.org... 

Also, for "SLL r" commands, those are newly documented opcodes, yes, but they 
are equivalent to the SLA command.  In an Arithmetic Rightshift (SRA), it has 
to preserve the 7th bit, the sign bit, and a Logical Rightshift (SRL) doesnt 
have to. The Arithmetic Leftshift (SLA) doesnt preserve anything, in a two's 
complement the 6th bit becomes the sign. A Logical Leftshift (SLL) doesnt 
have anything to do with the sign bits, so it also doesn't preserve the bits. 
 The only difference is how you want to look at the resulting number after 
doing a "SLL r" command: as an 8-bit byte, or a 7-bit integer with a 
sign-bit...

Jason_K