JoyMega support in OCM firmware ?

Prophet (2436)

21-05-2020, 22:37

Hi all,

I'm wondering if the famous JoyMega hardware modification could be integrated into the OCM firmware ?This could be a nice addition I guess ? It think it should remain optional to maintain compatibility with other MSX devices.

Maybe some attempts have already been done , what do you guys think ?

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Par ducasp

Paladin (677)

21-05-2020, 23:11

Unfortunately not, as PIN 9 is GND and it is hardwired to power supply GND and not to a FPGA pin, as such, it is not possible to input button C...

Even if you think to switch A/B button automatically as an example, by default an open button is +5V, so controller pin 9 (C or Start buttons depending on select) will be throwing 5V out of the 74157 directly to power supply GND, which could fry the mega drive controller circuit or the OCM or the power supply (probably it would fry the controller, but who knows)...

Par Louthrax

Prophet (2436)

21-05-2020, 23:19

Thanks Ducasp, that's clear. Subject closed I guess

Par hardwaremaker

Master (247)

22-05-2020, 12:22

I use JoyMega in the Zemmix Neo, without any problem.

Par sdsnatcher73

Prophet (3851)

22-05-2020, 13:49

hardwaremaker wrote:

I use JoyMega in the Zemmix Neo, without any problem.

The idea was that the JoyMega functionality would be integrated into the OCM firmware, so you would not need a JoyMega adapter and could connect a MegaDrive joypad directly to the OCM.

Par hardwaremaker

Master (247)

22-05-2020, 15:58

You only need to add 5 configuration jumpers, to switch between the legacy mode, and the JoyMega mode.

Par ducasp

Paladin (677)

22-05-2020, 19:23

hardwaremaker wrote:

You only need to add 5 configuration jumpers, to switch between the legacy mode, and the JoyMega mode.

Then it is not a firmware, but a hardware modification, but yes, a way to switch connections would be quite cool, a single switch that would make the port MEGA DRIVE compatible or MSX compatible.