Author Topic: Tobruk Dual CPC mode  (Read 522 times)

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Offline andycadley

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Tobruk Dual CPC mode
« on: 16:36, 30 December 20 »
The game Tobruk apparently has a mode on the CPC version in which two machines could be hooked up via a directly wired joystick cable and played in a two player mode.

I'd always assumed the joystick ports were read only, so I'm struggling to see how this could work. Has anyone ever tried it? Does anyone have any clues as to how this could work from a technical standpoint?

Offline ComSoft6128

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« Last Edit: 17:00, 30 December 20 by ComSoft6128 »

Offline 1024MAK

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Re: Tobruk Dual CPC mode
« Reply #2 on: 18:37, 30 December 20 »
Looking at the schematics of the classic (original) Amstrad CPC range, all the joystick lines except for the ‘common’ and ‘com 2’ are connected to the AY sound chip’s I/O port. These lines can be inputs or outputs. The only snag being that the ‘common’ and ‘com 2’ are open collector outputs controlled (switched) by the 74LS145 keyboard decoder chip, rather than real 0V/GND pins.

So for bidirectional signalling to work, one (or more) of the signal pins may need to be set low to act as (a) substitute 0V/GND pin or pins.

Then it should be possible to have two-way communication.

Looking forward to summer in Somerset :-)