View Single Post
Old 29th Jun 2015, 8:57 pm   #2
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: The Sinclair / Science of Cambridge MK14

Sinclair made some quiet progress throughout the life of the MK14 - I believe it eventually reached at least issue IV, possibly a couple of issues higher than that by the end. One of the improvements on the late marks was to (at last) bring out the address, data and control signals on the rear edge connector (the new contacts were added on the underside of the PCB, making what had been a single sided edge connector on earlier marks into a double sided one).

Prior to this, it had been virtually impossible to neatly install one of SOC's own main peripherals for the MK14, the 'VDU'. I had / still have this item as well. I have to say, it was not well thought out.

Apart from there being no official port or connector to connect it to on the issue II MK14, it also had no onboard memory of its own, stealing 512 bytes of the MK14's official maximum of 256+256+128 bytes of memory, leaving just 128 bytes in which to write your graphics-intensive power station control program.

I used my MK14 + VDU together only for a very short while, then restored the MK14 to largely original stand-alone condition (except for the keypad, which I had replaced). In 2013 I wired a PIC microprocessor PCB to the VDU card with the aim of at least being able to demonstrate it working without having to wire it back up to the MK14. (See attached image #1). Although I could theoretically use the down-time when the PIC is not serving data to the VDU to manipulate (animate) the screen data and make it do something interesting, it's one of those things I still haven't got around to doing.

One genuinely worthwhile improvement was the revised monitor (the one with the '0000 00' reset prompt, as opposed to the original one with the '---- --' prompt) - as well as needing far less individual keypresses to enter each data byte, it also incorporated the essential code to run the optional cassette tape interface, without which it was impossible to save any of your laboriously written code. You could use the tape interface with the original monitor, but you had to type some code in first!

I didn't have your original difficulty with working out how to enter code, but only because my MK14 took so long to arrive that in the meantime my similarly electronics mad friend had built the 'Elektor' SC/MP system - that was even more crude, with address and data entry by binary switches, but it introduced me to the basic concept so that I understood what I was supposed to do by the time the MK14 actually arrived. And after the Elektor system, the MK14's hex keypad entry and 7-segment display seemed like luxury beyond compare... until I realised how bad the keypad was.

The mounting holes for proper switches aren't present on my issue II PCB. I believe they were another improvement incorporated into the issue IV and I have a dim memory that suitable switches were made available as an optional upgrade kit by SOC themselves. I've also seen pictures of MK14s with clear plastic buttons fitted under the original black upper keypad frame and I'm not sure if this was also an official SOC improvement or something which was sold by a third party as an add-on.

Although the MK14's circuit diagram does show the diagram of the keypad it does not (as you rightly said) illustrate the connections to the keypad edge connector in sufficient detail. I have a crude self-drawn keypad diagram (attached image #2) - note that this specifically applies to the keypad edge connector on my issue II, it may be that later marks made use of the connections which I have marked 'N/C'. I always felt that the reset line should have been brought out to this connector as well, so you could mount an off board reset switch alongside your off-board keypad without having to clag the offboard reset switch connections onto the PCB itself.
Attached Thumbnails
Click image for larger version

Name:	IMG_6621.jpg
Views:	1417
Size:	61.3 KB
ID:	110138   Click image for larger version

Name:	mk14_keypad_v2.png
Views:	641
Size:	11.7 KB
ID:	110139  
SiriusHardware is online now