DDI-1 clone - some help needed

[unholy]

I have taken on the (overly ambitious) project of recreating the DDI-1 from scratch. (Don't ask. Needed a project. Seemed like a good idea.) Down the road, I want to incorporate a few small modifications into the design: +5VDC from the expansion port, floppy disk connector flipped around to standard pinout, 64KB ROM, reset and pause buttons. For now though, I want to replicate the basic design & see if I can get this thing off the ground. The problem is that all I have to work with is the schematic--no way to verify it against a functional unit. Here's my request then: is there a good soul out there willing to check a few connections on the DDI board for me? Specifically:

   
• IC112 (74LS74): verify that pins 6 and 8 are not connected to anything
• IC103 (74HC240): figure out what the "enable" pins (1 and 19) are connected to

Any help will be greatly appreciated.

[IanS]

IC112 (74LS74): verify that pins 6 and 8 are not connected to anything
IC103 (74HC240): figure out what the "enable" pins (1 and 19) are connected toAny help will be greatly appreciated.

IC112 Pins 6 & 8 are unconnected.
IC103 Pin 1 is linked to pin 10 (you can see that on some of the pics in the wiki). Pin 19 is linked to pin 1

[unholy]

Whoa, that was fast. Thanks much, mate.

[IanS]

Can be difficult to read, but the service manual has the pcb layout.
[attachimg=1]

[TotO]

Hello and welcome.

I got two questions:
- Is your 64K will be used for ROM0 + ROM7 ?
- Is a pass-through EXT connector is planed to plug other cards like RAM ?

Good luck!

[Bryce]

I can assure you that the schematic is exactly what's on the PCB, it has no mistakes or ommissions.

My suggestion: Add jumpers to allow ready signals to be made and a side switch, for people who connect a PC 3.5in drive to it, so that no messing around with the cable is necessary.

Bryce.

[unholy]

@TotO
- Yes. It's the mod described by IanS in this post. I just want to incorporate it into the layout.
- Not likely. I think it would complicate things a bit too much... but I'm open to suggestions.

I can assure you that the schematic is exactly what's on the PCB, it has no mistakes or ommissions.

That's good to know. Refreshing, too--these 8-bit era schematics are often riddled with errors. Also, the READY signal switch will be easy enough to add. Good idea.

Before I go any further with this--would anyone be interested in one of these? My initial instinct was simply to build a replica of the DDI-1 for personal use, but I would not be opposed to trying to make a small run of these happen...

[00WReX]

Hi there,

If it directly supports 3.5" drives, then yes I am definately interested. 

Cheers,
Shane

[IanS]

I guess it's easy to just keep adding ideas and end up with a huge shopping list of features.

My suggestions:-

Adding an ABBA switch, similar to the one posted by gerald - ABBA switch, the other way
Support either 64K or the original 16K ROM. If you end up making a few, people may want to run it with another ROM board.
Maybe add a simple way to disable the rom entirely.

[steve]

Could it work on the 464+?

[Badstarr]

As long as the Amsdos ROM is disabled as far as I know a DDI-1 should work fine with the 464 Plus.

[unholy]

Is there any practical reason to keep the CP/M autoboot and write precompensation jumpers?

[IanS]

Is there any practical reason to keep the CP/M autoboot and write precompensation jumpers?

The CP/M autoboot, just sets the ROM to be ROM 0, so if you make it with a 64K rom, that would be difficult to do. Not impossible, but probably not worth the effort.

You'd probably have to remap the roms so 4,5,6 & 7 became 3,2,1 & 0 (in that order) to autoboot. You could use the now spare XOR gates to invert the inputs to the 74ls74 for the upper address lines (A14,A15) on the 64K rom and invert D2 into IC110.

[unholy]

Hm. Which brings me back to the original question. I'm just wondering, does anybody actually use the autoboot feature?

[Badstarr]

I wouldn't think CP/M auto boot sees much use out there, the only benefit would be to auto boot a game or utility (or obviously CP/M) by pointing the loader to the appropriate file, some demos do this if memory serves. I would imagine that it could become rather annoying if every time you switch on your CPC it started searching for the CP/M system files. If you wanted a piece of software to "auto load" it would be better to use a ROM instead especially as we have the MegaFlash these days.

[unholy]

Update time. Behold, a (mostly) working prototype of the (somewhat) new and (slightly) improved DDI-1:

[attach=2]

Yeah, I know. I've had one of those "holy s#*t, I can't believe this actually works" moments, too. And yet, it's alive--and it actually needed very little in the way of troubleshooting. (I accidentally switched two signals on the FDD connector while transferring the schematics into Eagle. Believe it or not, it just happened to be the very first connection I checked. Talk about blind luck...)

Here's some "proof of life" photos: ROMs 4-7 reporting from the 27C512 EEPROM and the first loaded disk image:

[attach=3][attach=4]

Now, about the "mostly working" part... Manual image mounting/loading works just fine (though without an LCD it is something of a challenge), but I can't get the file manager to cooperate. It automounts just fine and I can load the front-end without a hitch. It detects the HxC, mounts the SD card, then announces "Access HXCSDFE.CFG file failed! [1]" and freezes.

I think I've gone through all the relevant options in the config file. I've tried both the disk and ROM versions of the autobooter. I've run it under AMSDOS and PARADOS. I've set the emulator as dive A and B. Nothing seems to make any difference. Any ideas?

[joska]

Impressive! That breadboard looks even worse than mine usual does    If you decide to make some interfaces for sale I'm definitely interested. I just got a couple of tiny laptop floppy drives that looks like they'll fit inside my CPC464.


Totally off-topic: Who made that SC1224? I have lots of ST/Falcon-stuff, and I have never seen a 1224 like this.

[unholy]

Totally off-topic: Who made that SC1224? I have lots of ST/Falcon-stuff, and I have never seen a 1224 like this.

I believe it was manufactured by Samsung.

[Gryzor]

My thoughts exactly! I didn't even recognise it, I thought it was hooked up to a TV... Looks nice, never seen one before either. This is what SC1224 looks like for me:


[attach=2]


back to the topic, very nice, congrats mate...

[duncan_bayne]

Before I go any further with this--would anyone be interested in one of these? My initial instinct was simply to build a replica of the DDI-1 for personal use, but I would not be opposed to trying to make a small run of these happen...

Yes!!!!!!     One of these, plus an SD card drive, and I'd be a very happy camper.