fieroluke

I hear ya! my latest revision of the board added SG1000 compatibility which I thought would have been cool, but complicated the layout even more of course! To simplify things I could have used programmable logic (GALs or CPLDs), but thinking this through you quickly end up with a FPGA version, and those already exist. The cool think about my concept (IMO) was that only an EPROM burner was needed to build it from scratch. Meanwhile I’ve created a 100% through hole Colecovision, with 64K Ram and 64K ROM, SGM compatibility and Basic, but not as a drop in replacement, but as a set of circuit boards on a backplane - 80s style.

I’ve halted development a few months ago. The reasons were: #1: My development board fried my wall wart power supply or vice versa, which killed my motivation. The 20 year old $5 wall wart maybe wasn’t up to the task and probably went overvoltage or something. I need to build a replacement. Reason #2 was the realization that it’s too difficult for 99% of the people to build themselves because of the miniature components. Reason #3: Having them made is going to be expensive, so the market is limited. I‘m considering adding value like a built in BASIC to turn it into an ADAMjr using The USB port to turn the host PC into a SuperDrive with keyboard, maybe making it a nice homebrew development platform.

I based my board on leaded solder‘s version. I think I found a missing connection somewhere in the roller controller interrupt circuit, but that was it. i liked the idea of leaded solder’s clean clock generation. As for the timing: it’s possible some assembler programmers relied on cycle counting but this isn’t 2600 programming fortunately, and the modern CMOS Z80 derivatives likely aren’t cycle accurate Z80 replicas. Remember, the games need to run on European VDPs at 50Hz as well, with very different video timings. i opted to add a selectable divider to allow 3.58, 7.16 and 14 MHz crystals. something I haven’t tested due to lack of equipment are driving and roller controllers. So if there is a bug in the weird roller interface with RC networks and transistors, that may still be in there. Regarding the weird audio: maybe you have a bad Audio chip? I’ve had a batch of 10 brand new ones come with a bad one.

I’m using an FTDI-USB-chip mapped to IO via a register. simple and reliable.

No, there’s no battery buffer… As I understand it, the SuperDrive was a tape running endlessly, and if the ADAM wanted to read a 1K block, it would have to wait until that block passed the read/write head, and if you read in sequence the wait times weren’t too bad. The tape would hold 256K in 256 blocks of 1K each. So that’s what I’ll recreate: the CV BIOS routine gets the block number to read, passes it to the PC, which then reads the proper 1024 bytes from the file and sends them back through USB, and the CV BIOS stores the 1K at the destination address. The BIOS increments all pointers so that by calling the routine again the next 1K is read to the next 1K in memory. Hopefully it will be easy to adapt the SuperDrive games to this. But the main benefit would be for developers who want to test on real hardware: just compile the code to a SuperDrive file, the PC exe will always read the latest version of the file, so you just need to press reset on the CV and the CV will automatically boot the new version from USB and execute it.

My mainboard has a USB client interface that can connect to a PC, Linux or Mac (or even Android). My mainboard also supports 64K RAM. The PC/Mac runs a program that provides one of 256 1K sectors, similar to the SuperDrive structure, boot sector is sector 0. That program hosts a file of up to 256K, the “SuperDrive Disk”, so to speak. My custom BIOS replaces the “insert cartridge” code with a bootloader that requests a 1K boot sector from USB, loads it to RAM and executes it. Plenty of space to enable the upper 64K (extended) RAM and load sectors from the “SuperDrive” to RAM. The ColecoVision has a routine in BIOS that lets the Coleco load one of the 256 1K sectors to any address in RAM, so the 1K bootloader can use that. But the bootloader could also bring its own USB driver and disable BIOS to have a full 64K memory map. I know it’s not exactly compatible with SuperDrive, but it is very similar, and using the standard boot code it’ll be a piece of cake to load non bank switch games of up to 32K to extended (upper) RAM. It should also be possible to port SuperDrive code to this.

Absolutely. right now I have two problems: finishing the BIOS for the USB SuperDrive and parts being unobtainable. That’s a problem with all electronics right now. Be it cartridge slots or simple things like capacitors. Sometimes there are inferior quality alternatives, sometimes there aren’t (for example with reset switches)… As for the BIOS: winter is coming (sigh) and with it more time…

🤣 no worries 😉

I think the thread is on the verge of being hijacked My full size drop-in replacement mainboard does retain the Quadrature controller, and has a ton of extra features. I’m working on Revision C, which will hopefully be the last one! mytek was talking about his miniature CV board…

I’m not using any PLD or GAL or anything. The whole point was to use use only TTLs and components that are readily available and don‘t require special programmers. i use an LS138 (like Coleco) to decode 8 8K chunks, the upper 4 are the 4 cartridge slot chip selects, the lowest one is the BIOS eprom chip select. This leaves 3 chip selects which you can combine using AND gates. If either input goes low, RAM CS goes low. That‘s 24K of ADAM RAM.I use an LS74 latch to disable the bios eprom if the FF is written and at the same time route the fourth CS to the RAM as well. So you have 24 RAM + 8K ROM or 32K RAM and no BIOS.

It's still not finalized. I'm working on what will hopefully be the "final" revision. That one features a VGA jack (in case an F18A is used) and I'm working on the USB-Based 256K "Superdrive". When it's all done, I'll publish the schematics and circuit board file so anyone who wants to can build one. To be honest, currently many electronic parts are not available and have lead times of 6 months or more. That doesn't help.

Finally got time to work on this project again. 1.) I ordered an Eprom burner so I can make BIOS mods at home. This should allow me to debug the USB support and develop the PC SuperDrive host, and eventually get the speech add on working. 2.) I hooked up my PAL Expansion module and I got audio and weak b/w video. Checking with a scope shows a really weak video signal, but directly at the TIA clone video seems ok. I’ll check out the buffer, possibly my eBay “unknown condition” purchase is shot but repairable. I found no documentation for the Expansion Module #1 PAL, so here are some findings for posterity: The expansion port goes to a small 16 pin flat flex cable. Busreq is pulled low to halt the Z80, Audio clock is pulled low to disable sound and VDP-reset is pulled low to disable video. The pinout of the FFC (useful for debug!) is: 1 /Reset (funny, because the EM1 has its own reset button!) 2 -5V 3 -5V 4 GND 5 +5V 6 +5V 7 +12V 8 EX-VID-EN (is pulled to ground in Expansion Module) 9 3.57 MHz Video Clock (not used in PAL Expansion Module!) 10 EX Video 11 EX Audio 12 not used/not connected 13 GND 14 GND 15 Expansion Port Pin 42 (NC) 16 Expansion Port Pin 41 (NC) So, the PAL expansion module needs even less than the NTSC EM1 for standalone operation.

I’m making slow progress, life getting in the way. I’m in the process of writing a USB bootloader that emulates a 256K tape drive. Not quite there yet. My EPROM burner is at work, so I have one attempt a week to burn a PROM and ultimately try out the next version of the modified BIOS…

True, but it can be found. Every Radio Shack used to carry that IC, I wonder where all those ended up?

Parts came in, so I could finally add port protection and more importantly: finish my speech add-on! It will be an interesting weekend with much-needed diversion…