I stated in the last issue that we ordered the Rotronics Wafadrive system from England. I also promised that I would give a report on it. Unfortunately, we have yet to receive it.
Anticipating it’s arrival I have prepared a Spectrum buss to plug the unit into. We have already received the operations manual and discovered that it will require a Spectrum ROM based 2068 (the ROM inside the drives begin where the operating system leaves off on the Spectrum which would “write” over part of the 2068’s operating system.) It will also require the R0MCS line and +9 volts which do not appear on the 2068. These will have to be generated somehow.
For R0MCS, the 2068 buss has a “not used” finger in the same position as where R0MCS appears on the Spectrum. I went inside my 2068 and connected a small wire between pin 27 of the ROM socket (U16) and the “not used” finger of the rear edge connector (pin 26 on the bottom side). It should be obvious which one it is because no solder lands lead away from this finger.
After this is done, that gives us 29 positions the same as the rear card-edge connector on the Spectrum. For the rest of the connections, I made up an extender card using a 28 position wire wrap edge connector and an extender caru cut to size (28 positions and one inch long) (Vector part number 3690) both available at Skipper Electronics. I keyed the edge connector and slotted the card in the 5th position as on the Spectrum and then proceeded to solder all the pins that were the same on both machines (see figures) to it’s corresponding position an the edge card. The remaining pins were cut back some so they wouldn’t short against anything.
To generate the +9 volts, I used a five volt regulator (#7805) and a 3.9 volt zener diode in series with the ground lead (diode cathode to ground lead) which references the 7805 voltage regulator at 3.9 volts thus giving a total regulated output of 5+3. 9=8.9 volts which is close enough. Tie the input leg of the regulator to +15v (pin 2 bottom side of the 2068.) Tie the output lead to finger 4 on the bottom side of the extender card and the anode lead of the zener diode to pin/finger 6 (ground) See figure.
Using as short as possible lengths of wire, connect signals from the 2068 buss to their respective positions on the Spectrum buss (see figure). The positions are numbered differently between the 2068 and the Spectrum, but everything is relative to the slot, so keep counting from there.
To save time and trouble, I only connected A8-A15, BUSRQ , RESET, and BUSAK. The -5 volts, +12 volts, and the -12 volts will probably be required for the RS232 part of the Rotronics, but we will worry about that later when we receive the drives.
Next Month: A printer interface you can build for the 2068!