UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Reply
 
Thread Tools
Old Yesterday, 4:25 pm   #121
Karen O
Heptode
 
Karen O's Avatar
 
Join Date: Jul 2011
Location: Bridgnorth, Shropshire, UK.
Posts: 663
Default Re: SC/MP timing and microcode information

On another aspect of SC/MP behaviour, has anyone EVER used a jump instruction that used a displacement from P1, P2 or P3? Is this useful for anything?
__________________
Karen O

Does Dr Who use Old New Stock parts for his/her Tardis?
Karen O is offline   Reply With Quote
Old Yesterday, 6:13 pm   #122
dominicbeesley
Octode
 
dominicbeesley's Avatar
 
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,833
Default Re: SC/MP timing and microcode information

Thanks for the NENIN pointers - that sounds about right though I'm wondering if NENIN is sampled at a clock edge to restart the cycle or just latched somehow. It being fed straight to the bus buffers sounds plausible and would make sens. I'll have to rig something up to try some really short pulses on NENIN to find out how it is latched or registered.

I was wondering about how calls into other pages are usually done. Is it usually with a XPPC?

I suppose the pointer relative jumps would be a nice way to do a vtable for object oriented code?
dominicbeesley is offline   Reply With Quote
Old Yesterday, 6:29 pm   #123
Timbucus
Hexode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 412
Default Re: SC/MP timing and microcode information

Quote:
Originally Posted by Slothie View Post
Quote:
Originally Posted by Karen O View Post
On this thread and the Mk14 VDU thread we were speculating whether the SC/MP NENIN input responds immediately or whether the SC/MP completes its current cycle before relinquishing.

I think I can say with confidence that it relinquishes immediately, probably via asynchronous logic so there's not even a clock delay. I think the SC/MP gets straight off the bus but takes note if it has been knocked back part-way through a cycle. It will try again when the buses subsequently become free again, perhaps multiple times. There must be a point in each memory cycle when the SC/MP deems 'mission accomplished' and ceases retries.

Do people concur with this analysis?
Now my inner sadist wants to stick a 555 on NENIN and see how it copes running a program.....
With a POT you could make a nice Slomo (remember those on the Spectrum) controller by varying the frequency...
Timbucus is offline   Reply With Quote
Old Yesterday, 6:57 pm   #124
Slothie
Hexode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 393
Default Re: SC/MP timing and microcode information

I'm currently designing a logic simulator that calculates timings so any info on the timing relationship between XOUT and transitions on NADS, NRDS, NWDS etc would help with making a waveform generator for SC/MP processors..... The data sheets are suspiciously vague on this as I believe you noted before.
Slothie is offline   Reply With Quote
Old Yesterday, 7:16 pm   #125
Mark1960
Triode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 32
Default Re: SC/MP timing and microcode information

Quote:
Originally Posted by Karen O View Post
There must be a point in each memory cycle when the SC/MP deems 'mission accomplished' and ceases retries.
From figure 4 of the datasheet it looks like NENOUT low indicates the cycle has been completed. But there seems to be no specific hold time between NENIN and NENOUT.
Mark1960 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 6:58 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.