A Tribute to the Dick Smith System 80
(aka Video Genie and PMC-80/81)

THE FreHDaptor - Another Fine Product From RAG ENTERPRISES

Proof that the System 80 never dies lies in the 2018 FreHDaptor. Here it is explained in Gary (Gazza) Howarth's own words...

Actually the FreHDaptor is the only product from RAG ENTERPRISES. RAG ENTERPRISES consists of Ray Whitehurst, Andrew Quinn, and Garry Howarth. The FreHDaptor is a board that plugs into an X-4020/EG-3014 expansion unit and allows the connection of a FreHD hard drive emulator to the System 80/Video Genie. It may also work with the Lo-Tech IDE adaptor but as yet no drivers have been written so that function remains untested.

Without going into all the gory details, the FreHDaptor takes the data, address and other signals from the expansion unit, shuffles them about and presents a Model III/IV compatible connector on the output. A 74LS245 is used on the data lines with pull-ups on all data, address and control lines. A 74HCT688 was used in an effort to stop corruption of the FreHD's RTC. A jumper was added to enable/disable the 74HCT688 and the board is powered by an SMD 5 volt regulator.

With the addition of a System 80 rom adaptor, a 2732 eprom can be used to replace the original E3001 rom and this will add a Boot Menu allowing the selection of either LDOS 5.3.1, NEWDOS 80 2.5 or DosPlus 3.5 operating systems.

The original work for this project was done by Ray and Andrew back in 2014 with Andrew designing the circuit and Ray building and testing the prototypes, all built on Veroboard. The details can be found on Andrew's site. http://www.quicktrip.co.nz/jaqblog/home/88-system80fhd1

The project then stalled until the middle of 2017 when we decided to resurrect the project, design a PCB and modify Dean Bear's Model I software to suit the System 80/Video Genie.

The FreHDaptor V1.0 was designed, built and installed and yes you guessed it, it didn't work - sigh Working on vintage equipment can be extremely frustrating, with broken wires, faulty connectors and the cheap single wiper sockets that EACA used causing me no end of problems, which resulted in a brain explosion on my part and the computer was back in it's box until my blood pressure returned to normal.

Having regained my sanity or whats left of it, I repaired the computer, expansion unit and tracked down the fault with the FreHDaptor which was nothing more than a faulty wiper on a brand new IDC socket. A new socket was installed and success, it all burst into life. Happy dance.

At this stage the new rom had not been installed and we still had to boot the computer from floppy but it was working and working perfectly, or so we thought. The FreHDaptor was left to run for a couple of hours and given a good test, checked out on the CRO and all looked good until I pressed the reset button. CRASH!!

MISOSYS never wrote a Model I version of the RSHARD package but a couple of guys from CN80 modified the Model III version to suit the Model I, unfortunately they missed a few things which resulted in the computer crashing when LDOS loaded the configuration. Another problem resulted in the directory being formatted with the date of 'MM/DD/YY' instead of the System date.

The offending problems were quickly found and eliminated and everything was working perfectly, or so we thought – again. On checking the time and date I found that the RTC in the FreHD had become corrupted. The battery showed over 3 volts so what had caused the corruption? Incorrect power-up sequence was the culprit. Powering the expansion unit and computer before the FreHD was causing the corruption and this was a problem that could be duplicated. Not always but enough to be annoying.

According to my notes, with the System/80 and X-4020 powered-up and the FreHD switched off, I was measuring 2.4V Vcc on the FreHD. Removing the 74LS245 from the FreHDaptor would drop Vcc to 0.32V Back to the drawing board and the FreHDaptor version 2.0 was born and this 'seems' to have cured the problem. As yet I've had no corruption of the RTC.

Installation of the FreHDaptor requires the addition of a 50 pin socket to P3 on the motherboard and the board is designed to fit into the supports on the base of the expansion unit.

Due to the oversized after market RS232 board that is fitted to my expansion unit, the FreHDaptor had to be designed to fit both my expansion unit and a standard unit. The final design is a bit of a compromise but it fits both perfectly, or close to it.

The next step was to get the Model I Boot Menu running on the System 80/Video Genie. I armed myself with a copy of Jack Decker's TRS-80 ROM ROUTINES DOCUMENTED, an image of both the standard System 80 rom and the modified Model I rom which I downloaded from Mav's site. HxD Hex Editor was then used to do a comparison of the two rom images and isolate the code for the boot menu.

A rom adaptor for the System80/Video Genie was designed that allows the use of a 2732 in place of the original Rom and being lazy I decided it was easier just to modify one of my existing Smartwatch designs rather than design a new board from scratch.

Yes, I did give in to temptation and fit a DS1215 but unfortunately the Smartwatch software could not find the clock.

Possible causes

  1. I've stuffed something in the design
  2. A faulty DS1215
  3. A software problem

The main thing is that it works perfectly as a rom adaptor and this computer already has two clocks so three would be a bit of over-kill.

A new rom was burnt, installed and on power-up I was greeted with the image below.

A nice feature of this version of FreHD.Rom is that it automatically loads the date and time on reset with the only modification made to FreHD.Rom being to change 'TRS-80 Model 1' to 'SYSTEM 80 V1.0'.

All of the FreHD utilities, VHDUTL, IMPORT2, EXPORT2 and DSK/DCT seem to be working reliably unaltered on the System 80 with no problems encountered – yet.

The addition of the FreHD and the Boot Menu has put some life back into the old System 80 and it has come a long way from it's original 16K of ram and cassette storage. Loading of any of the three supported operating systems is instantaneous and with about 60 Megs of storage for each operating system there is no shortage of space.

Many thanks must go to Andrew and Ray for doing the original hard work on this project and to Dean Bear, Fred Vecoven and all the other FreHD gurus that are helping to improve and keep these old machines running.


Added to the site 9th March, 2018

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