I was just looking at the inverse text display hardware mod on page 16 of the March 1988 issue of Dragon User. The mod takes the form of disconnecting pin 32 (INV) from the board and connect to pin 20 (DA11) through a SPDT switch. All very simple, but I would like to know for sure if this is the correct way to do this, and if its safe to switch between normal and inverse mode while the computer is powered up.
If the information is correct (and safe), it would be worth putting this mod in the "Hints and Tips" section.
Regards,
Steve
Inverse Text Hardware Mod?
Inverse Text Hardware Mod?
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Re: Inverse Text Hardware Mod?
It would force the inverted set certainly, but you wouldn't get dark-on-light for "lower case" characters. I think I'd want to make the switch optionally put DD6 through an inverter into INV, though I don't know if there are any spare inverters on the board that would make the mod so simple.
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Serenarian
- Posts: 29
- Joined: Thu Oct 25, 2012 1:28 pm
Re: Inverse Text Hardware Mod?
I've done this to all my Dragons in the past. The usual static precautions apply, but it isn't too difficult ...
You will need:
1. 74LS02 Quad NOR gate
2. Single pole Double throw miniature toggle switch
3. 1/2 metre of fine insulated wire
And here's how...
a) Bend up all the pins of the LS02 except pins 7 and 14.
b) Cut off pins 4,5,6,8,9,10,11,12,13 - leaving pins 1,2,3, and 7(gnd) and 14(Vcc) intact.
c) Bend pins 2 and 3 till they touch and solder together (pins 2 and 3 are the two inputs to one of the 4 gates on the chip - pin1 will be the NOT output).
d) Identify a convenient 14 pin 74LS series chip on the board that has pin 14=5V and pin 7=Gnd (74LS00,74LS02, 74LS04, 74LS08, 74LS32). On my D64 Rev3 it sits on IC9.
e) Piggyback your LS02 on top - soldering pins 7 and 14 onto the host chip.
f) Drill a small hole in the bottom casing (under the side alongside the keyboard is good) to mount the toggle switch.
g) Identify the 6847 chip (40 pins) and mark carefully pins 2 and 32.
h) Cut pin 32 as close to the board as possible and bend up the piece of leg attached to the chip until it is clear of the stump and track.
i) USING AN INSULATED/EARTHED SOLDERING IRON solder a wire from pin 32 of the 6847 to the middle pin of the toggle switch.
j) Solder a wire a second wire from the either of the other toggle switch pins to pin 1 of the LS02.
k) Solder a wire from the remaining toggle switch pin to pins 2 and 3 of the LS02.
l) Finally, and carefully, solder a jumper wire from 6847 pin 2 (don't cut the pin at all) to pins 2and 3 of the LS02
The toggle now selects Black on Green or Green on Black.
Now I know that they recommend forcing the outputs of all unused gates High to save current but I never bothered and had no problems.
You will need:
1. 74LS02 Quad NOR gate
2. Single pole Double throw miniature toggle switch
3. 1/2 metre of fine insulated wire
And here's how...
a) Bend up all the pins of the LS02 except pins 7 and 14.
b) Cut off pins 4,5,6,8,9,10,11,12,13 - leaving pins 1,2,3, and 7(gnd) and 14(Vcc) intact.
c) Bend pins 2 and 3 till they touch and solder together (pins 2 and 3 are the two inputs to one of the 4 gates on the chip - pin1 will be the NOT output).
d) Identify a convenient 14 pin 74LS series chip on the board that has pin 14=5V and pin 7=Gnd (74LS00,74LS02, 74LS04, 74LS08, 74LS32). On my D64 Rev3 it sits on IC9.
e) Piggyback your LS02 on top - soldering pins 7 and 14 onto the host chip.
f) Drill a small hole in the bottom casing (under the side alongside the keyboard is good) to mount the toggle switch.
g) Identify the 6847 chip (40 pins) and mark carefully pins 2 and 32.
h) Cut pin 32 as close to the board as possible and bend up the piece of leg attached to the chip until it is clear of the stump and track.
i) USING AN INSULATED/EARTHED SOLDERING IRON solder a wire from pin 32 of the 6847 to the middle pin of the toggle switch.
j) Solder a wire a second wire from the either of the other toggle switch pins to pin 1 of the LS02.
k) Solder a wire from the remaining toggle switch pin to pins 2 and 3 of the LS02.
l) Finally, and carefully, solder a jumper wire from 6847 pin 2 (don't cut the pin at all) to pins 2and 3 of the LS02
The toggle now selects Black on Green or Green on Black.
Now I know that they recommend forcing the outputs of all unused gates High to save current but I never bothered and had no problems.
Last edited by Serenarian on Sat Nov 03, 2012 8:05 pm, edited 1 time in total.
Re: Inverse Text Hardware Mod?
Thanks! 
It would be handy if you could post a duplicate of this in the Hints and Tips section.
Regards,
Steve
It would be handy if you could post a duplicate of this in the Hints and Tips section.Regards,
Steve