UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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.

Closed Thread
 
Thread Tools
Old 19th Nov 2020, 3:24 pm   #81
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: MK14 memory upgrade

The VDU itself only has a 12-bit address bus with the upper four bits selecting whichever 256-byte block of memory is being rendered from. If your proposed system will place RAM in the 0200-07FF area then I think it will be reasonable to decide that a continuous 512-block of that RAM will always be the VDU RAM and stick with that convention.
SiriusHardware is offline  
Old 19th Nov 2020, 11:19 pm   #82
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: MK14 memory upgrade

You should check out this article - I think it is my preferred approach to expanding the MK14 to NIBL etc leaving the existing base machine. VDU and expansion RAM as is - we just need to agree which 'hole' will be used...

https://archive.org/details/Personal.../2up?q=beefing
Timbucus is online now  
Old 20th Nov 2020, 9:31 pm   #83
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 memory upgrade

I was thinking to only buffer the address lines but playing with the layout in eagle it’s not too difficult to also fit a ‘245 data buffer. This then raises the possibility of a local and global bus. The MK14 and vdu would be on the buffered side as the global bus, the SCMP would only be kicked off the global bus by the vdu which would improve performance with the vdu active when running from local ram.

This is major feature creep but could open up some interesting possibilities.

I had thought about including the PIC16F877 in the expansion board, but I think it makes more sense now that it would be on a simpler module that could also be exchanged for a more advanced vdu. I kind of feel this also shows the elegant simplicity of the OrtonView as a single chip vdu replacement rather than bury it in a more complicated board.

I don’t think I’m going to be using a+b din connectors, but plan to use 2x32 dual row pin headers and socket headers, also not planning rack mount as these are too expensive.
Mark1960 is offline  
Old 20th Nov 2020, 11:02 pm   #84
Buzby123
Heptode
 
Buzby123's Avatar
 
Join Date: Oct 2011
Location: Culcheth, Cheshire, UK.
Posts: 637
Default Re: MK14 memory upgrade

The main problem with the VDU, either type, is the difficulty in co-operation with the 8060.

With auto-run downloaders and a VDU there is no need for the keyboard and LEDs. A set of replacement PROMs ( or a single EPROM on the extender ) could be programmed to co-operate nicely with the VDU.

Who uses any of the ROM routines in their code anyway ?.
Buzby123 is offline  
Old 20th Nov 2020, 11:34 pm   #85
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 memory upgrade

If I was going to make an expansion interface like that I would probably use JAMMA card edge connectors (28x2) since they are still easily available and cheap (~£2 on eBay, probably cheaper elsewhere). The only signals needed other than those on the CPU socket might be the power connections (the CPU power connections are not terribly beefy...) although there would be ample connector locations available for the keyboard connections, which might be useful. So you could have the interface card containing the CPU and the latches/mutiplexers etc to provide the upper 4 bits plugged into the backplane, with other cards connected to the backplane including the VDU (maybe an expensive DIN connector for that, since that seems to be the standard for that).

Mind you, if you're going to all that trouble you could probably make a SC/MP card to fit into a rack system like the Acorn System 1 and leave the MK14 as-is.
Slothie is offline  
Old 21st Nov 2020, 12:23 am   #86
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: MK14 memory upgrade

Quote:
Originally Posted by Buzby123 View Post
With auto-run downloaders and a VDU there is no need for the keyboard and LEDs..
With a VDU permanently enabled there is arguably no need for the 7-segment display, true, but surely there are always going to be some applications which require user input?

The MK14 has more key row / column intersections on its key matrix than are actually used so it is quite feasible to connect an alphanumeric keyboard to the keypad edge connector with up to 8 * 4 = 32 keys, although not quite enough for all the letters and all the numbers so there might have to be a 'num shift' key and some of the alpha keys doubling up as numeric keys.

It wouldn't be proper old-school, but it might make more sense to bit-bang an interface for a PC-AT PS/2 keyboard (with a mini DIN connector) - a lot easier to interface with than a USB keyboard.
SiriusHardware is offline  
Old 21st Nov 2020, 12:47 am   #87
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 memory upgrade

Quote:
Originally Posted by Buzby123 View Post
The main problem with the VDU, either type, is the difficulty in co-operation with the 8060.
I think one of the more interesting features of the 8060 is the way it can be kicked off the bus and it will repeat the cycle that was not completed. This could make it possible to put on the memory interface of a teletext chip or maybe even on a tms9918 with static ram. The microtan 65 type display is probably a more suitable option, with 16 rows of 32 characters is probably usable with NIBL.

It does look like the MK14 would quickly become a legacy IO module, but gives a historic progression from the MK14 to a more capable system. The expansion could easily run as a single board NIBL machine without the MK14.

I think I prefer pin headers over edge connectors. My second job was maintaining and programming testers based on 8085 in card frame with 43 way edge connectors and even with gold plated fingers they were always suffering from bad connections.
Mark1960 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:24 pm.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.