EXT port on model 1

[nathanallan]

Someone just posted that they have the pinout for this port on the original Genesis, and I'd love to use it for something. Is there any data out there about how to do this? Modems, linking consoles, anything? I'd love to null modem over to a PC if that's possible.

Nathan

[nathanallan]

It seems I have answered my own question about this. http://www.retrodev.com/transfer.html
So it's all good, now there's a new small project for me. :)

Nathan

[TmEE]

The EXT port is rather useless... a 3rd controller port with wrong gender that no game makes use of...
The software of that transfer suite does not let you choose which port you use (I think).
I use that cable in my MD dev stuff for MD and PC communication :)

[nathanallan]

This is now at the top of my projects list. Things I want to accomplish:

1. Establish MD to MD communication.

2. Establish some kind of link to PC. Why? See if I can play roms through that port and the second port of a Model 2.

3. Try and see what programs are out there to let me establish comms with a modem and then talk to either another MD or PC with another modem.

Because as far as I understand it, the thing is 1994-standards internet ready. I know it isn't much compared to today's net, but it's something. It's communication. And if it works, I say and always have make it work.

In the next few days I'm going to build myself that cable in that page, and also see if I can crossover to another MD, model 2 this time, since that's all I have at the moment (a Model 1 and a couple of Model 2's). I wish there were more hours in the day!!!

Along this train of thought, are there any roms that people have made that may make use of something like this?

Nathan

[Dirt Ball Gamer]

Would be sweet if you could play 2 player games online

[TmEE]

Things are not as simple !!! First you need to write a boot program which you load on flashcart or equivalent, and then you can think about reciving data... playing a ROM is impossible, unless you load the ROM on flashcart, or some RAM on the cart.... to get communication up, you need to write software to do that communication...
The ports(all 3) are bidirectional parallel ports of sorts, or slow (4800 baud I think, or 2400) serial ports using RS232C standard signal levels, so no direct connection to PC without +/-12V to CMOS line converter...

[nathanallan]

So it's not impossible. Maybe a little impractical, but that's never stopped me in any of my projects.

I actually emailed superfighter about this, and while Brandon didn't have any interest he did have this to say:



I see too much potential in the Genesis anyway, regardless.

Well, good! Go with that feeling. I did, despite everyone around me saying it was the dumbest thing they'd ever heard - and the result was Beggar Prince. :)

And I'm up to it, and invite anyone to be up to it too. Writing programs for a serial port isn't rocket science and has been being done for years. It's one of the most understood ports out there, and the most common, and I'm going for it. It may take a while but it's something I can really sink my teeth into.

Nathan

[TmEE]

Are you someone (unknown to me) MD/Genny homebrew developer ?

[nathanallan]

I tinker, and honestly I never thought I would be working with the Genesis. I never knew it had so much potential, though! What I have done so far is pretty much make every computer I own (a lot of them) talk to something else, be it a computer or game system or some sort of appliance. Mostly vintage stuff, which makes it cheaper and more interesting since there's very little support for it.

I hope I don't come off confrontational, I don't mean to. I just like to squeeze every bit of capability out of my hardware.

My two main and most fun projects I have done so far are making my Atari ST talk to a Unix server and crappy windows laptop talk to my Epson computer. That was fun stuff. Challenging, too!

[TmEE]

well, good luck learning 68000 if you haven't, and MD VDP then :)

[nathanallan]

What I have learned so far:

The EXT port on the model 1 is a kind of cut-down parallel port.

There were lots of attempts back in the 90's to make modems, whole bolt-on systems for making the Genesis talk online, including AT&T.

So far as far as knowledge base, that's pretty much it. I have learned that there is a BASIC for the 68K proc, but mainly only rumors. I haven't found a compiler yet.

Luckily, I have another Model 1 on the way so I won't have to build any kind of logic stuff to make up for it on the Model 2. if there is any lack, I'm concentrating on the Model 1 for now. I'll get to the M2 when I get to it.

Still looking for roms that take advantage of the port, if there are any. Also, must buy a flash cart from tototek, unless I can figure out how to make something like it myself.

The pinout tells me that the cable may not need any kind of crossing, but something else may be needed. Unlikely it would be a straight cable.

I also have a lot of emails out and have searched a bunch of websites on this. I know a little bit of C from tinkering with the Atari ST computers, but not nearly enough. That BASIC would be great if I could find it. It's late, still looking.

Nathan

/edit found BasIegaXorz (http://devster.monkeeh.com/sega/basiegaxorz/), a basic compiler for the Genesis. Now, only a flash cart remains.

[TmEE]

The EXT port hardware is identical to Controller ports, only difference is the gender of the D9 connector... all ports feature 4800 baud bidirectional serial capabilities (but no handshaking AFAIK) and 6-bit bidirectional parallel, direction of each bit can be configured independently. Its is much feasible to use LPT port rather than COM port, as the voltage levels of PC COM ports are 2x higher than of your MD, and you will kill your MD (at least partially).

Good luck with BasiEgaXorz.

[nathanallan]

I joined the forum over there at Devster and hope that will help, pretty sure it will, they're a pretty technical bunch. Thanks for pointing those points out about the port. I might have fried something. This is interesting.

[TmEE]

gendev.spritesmind.net/forum

All the serious MD dev people live in that forum... Devsters forum is a bit dead... only real thread where some action happens is 386 supertuning thread... cool thread though

[dragonboy]

here is a map of the insides I found:

http://www.emu-docs.org/Genesis/mega3.png

hey, I thought the Genesis had 64 kilobytes of ram, but this only says 32k?

[TmEE]

there's 2 chips.... 32+32=64

and that block diagram is not very useful... what is required is programming manual and these are available all over the net.

[nathanallan]

Something has occurred to me. While the Genesis would be hard pressed to process network handling and a game at the same time, a game of the same nature and the network stuff would be easy for it with the CD attached. From wikipedia, here are the CD specs:

CPU

The main CPU is a 12.5-MHz 16-bit Motorola 68000 processor. The Mega Drive has the same processor, but at a lower clock rate of 7.67 MHz (NTSC) / 7.61 MHz (PAL). In the combined system, both processors run concurrently for Mega-CD games, and the Mega-CD processor is idle for Mega Drive games.

Graphics

* Graphics Processor: Custom ASIC
* Number of simultaneous colors on screen: 64 out of 512
* Display resolution: 320 x 224 pixels and 256 x 224, video size from ¼ to full screen
* Advanced compression scheme
* Software-based upgrade
* Scaling and rotation effects

RAM

* Main RAM: 6 Mbit (upgrade from the Mega Drive's 64kbyte)
* PCM samples: 512 kbit
* CD-ROM data cache: 128 kbit
* 64 kbit Internal Backup RAM (for storing saved games, scores, etc. for CD games)

Storage

* 500 MB CD-ROM discs (equivalent to 62 minutes of audio data)
* ¼ screen B/W footage video: 1.5 to 4 hours
* ¼ screen color footage: 45 minutes
* CD-ROM drive transfer rate: 150 kB/s (1x)

(Above specs prior to compression)

BIOS

* Size: 1 MBit
* Used for games, CD player, CD+G and karaoke
* Access time: 800 ms

I am going to change my scope here on this project to include the Sega CD as well as a standalone Genesis. Also, it is my theory that the dongle that came with the 32X systems (some of them at least) was a way to clean up electrical noise, and this would be needed for networking this thing. Offline it is useless, but online it would be necessary.

Nathan

[matteus]

errr have you actually ever programmed for the genesis? :p

[nathanallan]

No. I do intend to learn it though.

[tomaitheous]

If you want to do anything serious, I recommend skipping that basic compiler and going straight to assembly. If you've never used assembly before, then let the 68k be your first processor. The 68k is pretty easy to understand and use ;)

[nathanallan]

If you want to do anything serious, I recommend skipping that basic compiler and going straight to assembly. If you've never used assembly before, then let the 68k be your first processor. The 68k is pretty easy to understand and use ;)
Can you recommend ant decent books? I have a few books on the Atari ST since it uses a 68K. They're all GEM and geared specifically to the ST, though. Older text books maybe? Some with lots of exercises so I can practice a bit.

Nathan