segmented memory models
dkelvey at hotmail.com
Mon Aug 4 08:59:23 CDT 2008
> 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.
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
Your PC, mobile phone, and online services work together like never before.
More information about the cctalk