FRS' MSX page WIP

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By Grauw

Ascended (8742)

Аватар пользователя Grauw

09-02-2020, 13:27

Oh, I see, a shame the protocol is different! They look so similar.

And yeah I already have a wireless 8bitdo Smile. At Nijmegen I was also recommended this wired controller which is officially licensed by Sega and apparently really good quality. They’re sold in Europe in various shops (e.g. nedgame.nl) as Retro Bit MegaDrive (do a google shopping search).

By Louthrax

Prophet (2172)

Аватар пользователя Louthrax

09-02-2020, 14:04

sd_snatcher wrote:

For those who are after a cost/benefit solution, these joypads are cheap and have a pretty decent quality. They not come close to the 8bitdo quality, but are pretty usable nonetheless.

Hi Snatcher,
Those are indeed very cheap. Do you know if the PCB quality is decent too ? I used to buy some really hyper-crappy Megadrive joypads from eBay just for the PCB (in order to solder arcade-style controls on it), before reallizing the PCB was cardboard, bending with temperature / age and humidity, and not working after some months (maybe the crappiest things I've ever bought on eBay, even if that was only 2€ or so...). So I now have a couple of arcade joysticks on which to change the PCB and solder again...

By sd_snatcher

Prophet (3246)

Аватар пользователя sd_snatcher

09-02-2020, 15:54

I took the liberty to move the joypad conversation to its specific thread. This way it won't derail this one, and it will be easier to keep track o this subject on that thread. :)

By sd_snatcher

Prophet (3246)

Аватар пользователя sd_snatcher

12-03-2020, 01:14

I've published the revision-3 of the joyMega adapter (or joyMega3, for short). It adds diodes for the pins 6 and 9 of the Megadrive controller, to protect against bus contention if the pins 6 and 7 of the MSX joystick connector are configured for output (i.e., if PAD(0) is used on MSX-BASIC).

If you have an older revision of the joyMega adapter, it's highly recommended that you modify it to add the diodes, otherwise the MSX or the controller might be damaged if the PAD(0) or PAD(4) functions are used on MSX-BASIC, or the respective GTPAD(0)/GTPAD(4) are used on assembly. Many softwares like Philips Video Graphics, Philips Designer, Philips Designer+ will do it on the joystick port2.

By gdx

Prophet (3320)

Аватар пользователя gdx

12-03-2020, 14:22

Why do you think diodes are needed here? Controllers with chips for autofire don't use diode.

http://www.msx.org/wiki/Panasonic_FS-JS222

By spacemoai1973

Master (165)

Аватар пользователя spacemoai1973

12-03-2020, 18:11

Nice idea to put diodes, but shouldn't they be reversed?

By sd_snatcher

Prophet (3246)

Аватар пользователя sd_snatcher

12-03-2020, 19:52

@gdx

As I explained, the diodes are needed because of the risk of bus contention.

Without the FS-JS222 schematics, it’s hard to know how it’s implemented. But judging by the PCB picture, I suspect that it uses the transistors for this protection job.

@spacemoai1973

The normal logic level of the pins 6 and 7 is 1. Only when they’re configured to output 0 and the Megadrive controller outputs 1 (released buttons) the bus contention will occur. This means that the cathode side of the diodes must be connected to the controller. :)

By gdx

Prophet (3320)

Аватар пользователя gdx

13-03-2020, 12:32

Look at the MSX Service Manuals. Device connected to a general port has pins 6 and 7 directly linked to the inputs of a 74LS157 and to the outputs of a open-collector 74LS09/7407 with each a pull-up resistor. So even if pin 6 and 7 are set to output there is no conflict and even less the possibility of damaging the PSG. Diodes are useless.

By sd_snatcher

Prophet (3246)

Аватар пользователя sd_snatcher

15-03-2020, 04:27

gdx wrote:

Diodes are useless.

This is a very strong opinion that demoralises the solution and those involved. Here we have one of those moments where either the person stating it is a genius that know something that everyone else on the field isn't aware of, or the sentence is just pure DUPO (Destructive Uninformed Personal Opinion). Similar to anti-vaxxers and flat-Earthers.

Are you sure attention is being paid to the details? This is the basic Megadrive controller schematic:

If you look at the 74xx157 datasheet, you'll see that the outputs of this chip are not open-collector. They're push-pull. Now, take a moment to analyse: what do you think will happen if either the pin-6 or pin-7 of the MSX joystick port are set to output ZERO, and the Megadrive has all it's buttons released (not pressed)?

The diodes were added to convert the Megadrive joypad pins-6 and pin-9 outputs to open-collector before they're routed to the MSX pins-6 and 7 respectively. This way there will be no bus contention in this situation.

The diodes are useful. DUPOs, OTOH are definitely not useful nor productive. They consume time to clarify the facts, demotivate and are the antonym of healthy human relationships.

When not sure about the usefulness of something, asking in an educated manner will prompt an educated reply. The opposite also applies.

By gdx

Prophet (3320)

Аватар пользователя gdx

15-03-2020, 09:27

I did not write that 74xx157 are open-collector. It's not necessary because these are inputs that are used. This is the 74LS09/7407 that is open-collector. On Turbo R and probably other MSXs with integrated chips, they had to use a method other than the open-collector (bridge of diodes zener and an other component on each line). I think they didn't put it to decorate. I say this to save you from putting components for nothing. I'm not a professional but I'm pretty sure of myself. Do not get upset and give more convincing arguments if you are sure otherwise.

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