The Premier Sprite Board
This story really starts with the Premier Sprite board, first mentioned on the World of Dragon forums back in January 2019. That board was actually developed by Premier Microsystems back in the 1980s for their UK101 computer system, and it was adapted to work with the Dragon 32. There were articles on the board in Dragon User and Personal Computer News.
It turned out that David Linsley actually had two Premier Sprite boards which he photographed and posted to the WoD forum. The Sprite board was essentially a TMS9929 VDG chip coupled with 16K of DRAM, a BASIC extensions ROM and some analogue video circuitry.
There were some known limitations to the Premier Sprite board – the main one being that it could not work with a Dragon 64 and did not have a very rich BASIC extensions; although LINE and CIRCLE had been implemented, neither DRAW or CIRCLE were – limiting the usefulness from BASIC.
Discussions started around reproducing the boards, and I confess I was initially not that interested, due to the above limitations. It didn’t really feel worth bothering with if it wasn’t fully compatible. That initial disinterest didn’t last long. I reversed engineered everything I could from the pictures posted to the forum. Due to the amount of tracery underneath those awful 1980s IC sockets I was not able to progress further until David attended the July 2019 Dragon Meet-up where he loaned the boards to me for me to try and get them working.
As can be seen from the images above, the neutral coloured board was populated with more chips, and seemed to be more complete. I spent a long time trying to get this board running to very little avail. Whilst the neutral board had all the hallmarks of a prototype board, the green boards looked more like production boards. I therefore decided to strip the green board right back to get a decent look at all of the tracery.
Some months later (December 2019), I revisited the Sprite board and rebuilt the green one from scratch using some new components. I also wired the cartridge port to DIP socket again from scratch – and lo and behold, the board worked. For possibly the first time in 35 years, we were able to see the device working, video it and share it with the Dragon Facebook group.
Whilst this was an exciting moment, the graphics on show were not earth-shattering. And it was also realised that not only would the Sprite board not work with a Dragon 64 – it could also not work with a disk interface of any kind – mainly because of the onboard ROM for the BASIC commands.
All Hail the WordPak 2+
Mike Miller mentioned the WordPak 2+ board to the group, which was based upon the V9958 VDP. This chip was supposed to be backwards compatible with the TMS9929 (which was a PAL variant of the TMS9918). The WordPak 2+ board had been developed by CocoDemus, was designed primarily to work with a Coco 1 or 2, and to fit into a Tandy ProgramPak cartridge.
The design was freely available for others to use, and the PCBs were available from a Russian supplier. One quick jaunt around AliExpress and a couple of V9958s, some SDIP64 holders and twenty or so memory chips were on their way from China. The board used one seemingly obsolete component – a 74S133 – which is a 13-input NAND gate. Nevertheless, I managed to get hold of 24 of them for around £5.
One difficulty I encountered with the WordPak 2+ board was the video connection. The DSUB-15 socket was non-standard and the output was designed for 15 Khz monitors. Pere Serrat already had one of these WordPak 2+ boards, but had not used it by this point. Bas Gialopsos came to the rescue of both of us by showing us how to create this custom cable.
My first cobbled together cable gave an appalling output. It clearly was not well enough screened. After buying a full 21-to-21 connector from the UK store, Argos, I thought it would be easy to adapt. However, upon opening one end of the cable, I discovered a big problem. The SCART plug cabling had been completely glued in place for robustness – but more frustratingly, every cable inside it was pink!!
Not to be deterred, I set about making my new cable the hard way – buzzing out every pink wire until I found the ones I wanted, and then connecting into my DSUB-15 plug. It was difficult, but it was a success.
To be continued…