DragonCoCo
Posted: Wed Oct 03, 2012 9:46 pm
Cop[y of what I just posted to the CoCo mailing list as it may also be of interest here.
Hi all,
I've just managed to modify a Dragon 64 to be dual personality, both as a Dragon 64 or a CoCo.
This involves two circuits, one is a 27256 (or bigger) that replaces IC18, and has the normal Dragon rom in the lower 16K and a slightly modified** CoCo 2 rom in the upper 16K, A14 is connected to a switch so that you can select between them.
** The reason for the modified rom is twofold, firstly the Default CoCo rom writes to one of the PIA echoes in the FF04-FF07 area, on the Dragon 64 this is where the ACIA is mapped, so this has to be avoided.
The second reason is that the CoCo 1/2 have to detect what RAM chips are fitted (as does the Dragon 32), whereas the Dragon 64 will always have 8x4164 64Kx1 chips, so the ram detection code is removed.
The other part of the circuit is a little board containing 2 4053 analog multiplexors, that sits in the keyboard cable and who's job it is to re-map the Dragon keyboard layout onto the CoCo one. The select inputs for these two chips, pins 9,10 and 11 are wired together and connected to the A14 switch of the rom circuit.
There is one mod to the main board that is required for this to work, C5 and C2 must be removed, on the Dragon these sit between the PA0 and PA1 lines of the PIA and ground, these are the lines the joystick buttons are connected to, without removing these the first two rows of the keyboard will not work in CoCo mode. The CoCo has these two caps on the other side of the L1 and L2 inductors inline with the buttons, so it may be possible to re-connect them there.
Note at this time I have done no testing of how this affects the joystick.
This way I can power on with the switch in one position and I have a Standard Dragon 64, which will play nicely with standard Dragon programs, and will boot into all ram basic by typing EXEC 48000. In the other position I have a CoCo 2, with 64K CB 1.2 and ECB 1.1.
I have designed a circuit that will hopefully plug into the printer port and convert it to a bit-banger, which will work in CoCo mode, though if the correct software where written there's no reason it shouldn't also work in Dragon mode.
Please also note that all the above was done on a UK Dragon 64, I do have a couple of Tano machines, so at some point I'll try it on them but see no reason why it would not work. However some of the components may be labeled differently.
Cheers.
Phill.
Hi all,
I've just managed to modify a Dragon 64 to be dual personality, both as a Dragon 64 or a CoCo.
This involves two circuits, one is a 27256 (or bigger) that replaces IC18, and has the normal Dragon rom in the lower 16K and a slightly modified** CoCo 2 rom in the upper 16K, A14 is connected to a switch so that you can select between them.
** The reason for the modified rom is twofold, firstly the Default CoCo rom writes to one of the PIA echoes in the FF04-FF07 area, on the Dragon 64 this is where the ACIA is mapped, so this has to be avoided.
The second reason is that the CoCo 1/2 have to detect what RAM chips are fitted (as does the Dragon 32), whereas the Dragon 64 will always have 8x4164 64Kx1 chips, so the ram detection code is removed.
The other part of the circuit is a little board containing 2 4053 analog multiplexors, that sits in the keyboard cable and who's job it is to re-map the Dragon keyboard layout onto the CoCo one. The select inputs for these two chips, pins 9,10 and 11 are wired together and connected to the A14 switch of the rom circuit.
There is one mod to the main board that is required for this to work, C5 and C2 must be removed, on the Dragon these sit between the PA0 and PA1 lines of the PIA and ground, these are the lines the joystick buttons are connected to, without removing these the first two rows of the keyboard will not work in CoCo mode. The CoCo has these two caps on the other side of the L1 and L2 inductors inline with the buttons, so it may be possible to re-connect them there.
Note at this time I have done no testing of how this affects the joystick.
This way I can power on with the switch in one position and I have a Standard Dragon 64, which will play nicely with standard Dragon programs, and will boot into all ram basic by typing EXEC 48000. In the other position I have a CoCo 2, with 64K CB 1.2 and ECB 1.1.
I have designed a circuit that will hopefully plug into the printer port and convert it to a bit-banger, which will work in CoCo mode, though if the correct software where written there's no reason it shouldn't also work in Dragon mode.
Please also note that all the above was done on a UK Dragon 64, I do have a couple of Tano machines, so at some point I'll try it on them but see no reason why it would not work. However some of the components may be labeled differently.
Cheers.
Phill.
