VIM Q again

[Rick Stevens]

Mikkel L. Ellertson wrote:
> Cameron Simpson wrote:
>> On 02Jun2008 02:09, Gene Heskett <gene.heskett at verizon.net> wrote:
>> | Jump tables scattered around in your code, taking up valuable space 
>> cuz the | darned thing doesn't have a conditional long branch ability, 
>> just for starters.
>>
>> Hmm. I don't seem to recall needing jump tables, but perhaps my code
>> was smaller than yours. In fact, I've got some z80 code right here [...]
>> The long jump JP command allows conditionals. The 8080 might not have;
>> I never used that, either.  I did have a Z80 macro for measuring the
>> length of the jump and using a JR instead of a JP where possible, but
>> JPs definitely allowed conditions.
>>
> The 8080/8085 had jump to an absolute address, with or with out 
> conditions, but did not have the jump relative that the Z80 did. So even 
> for a jump of 126 bytes away, you had to use the 3 byte jump instructions.

The Z80 had:

	JR idx(unconditional)
	JR Z,idx (jump relative if zero)
	JR NZ,idx (jump relative if non-zero)
	JR C,idx (jump relative if carry)
	JR NC,idx (jump relative if non-carry)

And one of my favorites for loops:

	DJNZ idx (decrement and jump relative if non-zero)

So, yes, the Z80 had conditional relative jumps.  It also had that nice
set of secondary registers...very handy for interrupt processing.

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- Rick Stevens, Systems Engineer                       rps2 at nerd.com -
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