segmented memory models

[dwight elvey]

> From: cclist at sydex.com
>
> On 4 Aug 2008 at 1:19, Roy J. Tellason wrote:
>
>> I'm a little curious about all those restart instructions, anyhow, and why I
>> never saw any real use of them much. I seem to recall one of them being used
>> for a debugger and that was about it. Then there's the extra ones you get
>> with the 8085. Anybody know of other uses for those?
>
> There aren't any "extra" RST instructions for the 8085, just new
> vectors. Recall that the 8085 has several external interrupt pins
> (IRQ 5.5, 6.5 and 7.5), which simply simulate calls to locations
> 002C, 0034 and 003C respectively.
>
> One early use for the RST instructions was before the day of the 8259
> PIC. You could implement a rudimentary vectored interrupt scheme
> with a priority encoder and a buffer to gate a 1-byte RST instruction
> as part of the interrupt acknowledge protocol. Note that the RST
> instruction takes the form 11nnn111, where nnn is the "number" of the
> RST. A hangover from the 8008, whose RST was encoded 00nnn101.
>
> Cheers,
> Chuck
>

Hi
 RST's were useful to start up an output interupt as well. Depending
on hardware, these might not self start. One needed a first output
to start things. By using the same vector, one didn't need to duplicate
code.
Dwight

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