Denial

I've always been wary of building or buying a Plus/4 joystick adapter because of people blowing out their TED in some cases. As I understand it the Plus/4's joystick port it very different than the C64/VIC-20 etc. because it uses a "Select" line to select the joystick to scan. I didn't like the idea of just shorting the select line to the direction pin. Then I came across the schematic below. This uses a 74ls244 buffer/line driver with enable pins. The select line is connected to the enable pins to allow output only when necessary. I also used 220ohm current limiting resistors instead of the ones shown. It works fine, but being paranoid about the TED chip, I'd thought I'd ask if anyone has an opinion. Thanks.

i'd perhaps even use 470Ohm - but looks OK to me

Thanks for the suggestion. I will give it a try, that's one thing i was thinking about. It's on a breadboard now so it's easy. It is well known that it's almost impossible to find a TED chip so I don't want to be the cause of it's demise. And I had to try this new game - Pets Rescue. It's pretty good so far. I got this Plus/4 for only $5 shipped (basically free) 15 years ago and when I got it all the memory chips were bad - every one. Everything else including the power supply was fine. It was strange.

perhaps even try higher values... you shouldnt need much current (almost none) afterall

and yes 15 years ago it was easy to get deals like that... i wish i had got myself a stack of plus4 and vic20 too.... i only got a dozen C64s and drives

Yeah, I will try a few. The 244 is pulling the lines down, I'll use a scope to find the best value now.

When I made my adapters I followed a description which had resistors on all the direction/fire lines I think for the purpose of protecting the TED chip in some way. Anyway, I thought I was smart and reduced all those resistors to just one (on the return line or whatever it's called), and it seemed to work at first, but... when moving the joystick in a diagonal plus pressing the button (three at once so to say), it didn't work, it just flickered between two states. So I performed some surgery and just bypassed that resistor ... I think it should be safe with a simple adapter like that as long as you don't use any autofire or something like that.

I just wanted to follow up on this..I made a final version that contains the 74ls244 and resistors on a mini PCB attached to a DB9 male connector and enclosed in a 3d printed case. The wire is a Apple Mac serial cable - It is the correct mini DIN. I ended up keeping the 220 ohm resistors in the design. This should work with Auto-Fire joysticks without worry because with this circuit, the computer is reading the joystick at it's own pace because the select line is properly implemented and thus will prevent contentions.

As soon as I get my time machine to work, I'm going to beam back to 1983 (before the release of the Plus/4) and slap some sense into Commodore.

Commodore! WTH? Use a standard Atari 2600 style joystick like the rest of the world!

**EDIT**

Crap. I just realized that if I convince Commodore to not use that proprietary joystick adapter then in 2018 we wouldn't be having this discussion. And I wouldn't need to travel back to 1983. But if I never travel back to 1983, I would never talks some sense into Commodore.

Daggum paradox!

Seriously...what you created is a great option. I like the idea of the buffered chip. Seems much safer to me.

norm8332 wrote:I made a final version that contains the 74ls244 and resistors on a mini PCB attached to a DB9 male connector and enclosed in a 3d printed case. The wire is a Apple Mac serial cable - It is the correct mini DIN. I ended up keeping the 220 ohm resistors in the design.

Very nice.

As soon as I get my time machine to work, I'm going to beam back to 1983 (before the release of the Plus/4) and slap some sense into Commodore.

You mean CBM engineer Bil Herd. He's right there in New Jersey.

Truly,
Robert Bernardo
Fresno Commodore User Group - www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - www.portcommodore.com/sccan
June 9-19 Pacific Commodore Expo NW 2018 - www.portcommodore.com/pacommex
Aug. 11-12 Commodore Vegas Expo v14 2018 - www.portcommodore.com/commvex

RobertBe wrote:You mean CBM engineer Bil Herd. He's right there in New Jersey.

Nah. Bil seems like a good lad. And I'm sure upper management at Commodore had something to do with that decision.

From what I read the decision for the smaller joystick-port was due to the C116. This was going to be the $50-computer to compete with the ZX Spectrum. However the 9-pin-plugs would not allow for the small case, so they came up with the smaller joystick-port which was then also used on the C16 and PLUS/4.

I'm not sure if normal joystick ports would fit on/in a Plus/4 either. It's pretty packed.

FWIW, I think the Plus/4 is the most attractive 8-bit computer Commodore ever did. I love the design of it for the most part.

I got the schematic for this from http://www.commodore.ca/manuals/funet/c ... s4joy.html

The only change I did was changing the resistors to 220 ohm. It works perfectly, I ended up making two.

I'm attaching the entire project including 3D files and an eagle PCB for a home-brewed PCB in case someone wants to make the same one.