Eurocom-I and my descendants
What is it?
The Eurocom-1 is a computer created by Eltec and is an SBC with a small keyboard and some 7-segment displays like the Commodore KIM and Microprofessor. It uses a Motorola 6802 as processor, contains 2 * 2 KB of ROM, 1 KB of RAM plus I/O. I created a new version plus descendants.State: Schematics, board and PCB.
Background
In the years 1983 to 1987 I studied at the HTS, technical university (?), in Heerlen (NL) and we used the Labbus, a computer equiped with the 6809. But it was quite new then, its predecessors was still in the training area: the Eurocom-I from Eltec. Some years ago I was given one by Fred Jan Kraan and I decided to dedicate a page to it.6809 CPU
Eltec also created the Eurocom-II, a board equipped with the 6809 CPU. Note: there are several different version around.
But as you can see, it lacks the displays and keyboard that the Eurocom-1 has. Eltec also created a small board equipped with a 6809 meant to replace the original 6802 on the Eurocom-I board. I have no idea if Eltec created this replacement board before or after creating the Eurocom-II.
Anyway, I wanted to document everything of the Eurocom-I, especially the schematic. During creating this page the idea rose to create a better version of it.
A description of the original Eurocom-1
The main features of the Eurocom-I:- Motorola 6802 CPU: same as the 6800 plus 128 byte on board RAM.
- Supports 2 * 2 KB of 2716 EPROM.
- 1 KB of RAM
- 2 * 6821 PIAs, one for the keyboard and displays, one free one.
- one cassette port with a 6850 ACIA as core part.
- Two 64 pin AC-DIN connectors.
- RAM at $A000, I/O at $8000.
- A 4020 counter is used as interrupt generator.
The schematic:
My idea of the Eurocom-1
- As above, the same 6802 CPU.- 2764 8 KB EPROM but only 6 KB wil be used. Using a 2764 also means I can use a 27C256 EEPROM.
- Needing up to 56 KB of RAM, I chose for using a 128 KB RAM. Main reason: I only need one IC.
- The cassetteport is removed but the ACIA is kept. A 1,8432 MHz oscillator replaces the original clock generator. A header is added for the typical RS-232 signals but I'll use them only in digital form.
- The 4020 is replaced by a 74LS393.
- A GAL is used to choose the addresses for the ROM, RAM and I/O. Advantage: the configuration can be changed when needed.
- Yo be able to make use of the various Elektor cards I own, I added a 64 pins male AC DIN connector. This enables me to connect an expansion bus from the left site of the board, which on its turn enable me to connect various Elektor expansion boards like the RTC, Floppy controller and video card. The only disadvantage of the place of the connector is that the board cannot sit in the original case anymore if you want to connect a bus.
The schematic:
The board:
The Eurocom6809
The creation of the schematic was relatively simple: just replace the 6802 with a 6809. The 6809 does not have a VMA line but it could be created with some gates. The MicroKit09 does only use the E signal to synchronize the CPU with the ROM, RAM and I/O and I have living proof that that works fine. So I decided to keep it simple and drop the VMA line completely.The schematic:
The board:
The actual board:
The software
I cannot use the software of the original Eurocom-I as it written for the 6802 CPU.The German magasine CHIP published in November 1983 an article about this 6809 board including the hex listing of the ROM. I tried to OCR the article but in the end I had to type in everything by hand, just like the "good" old days. I tried to disassemble it but I ran into a weird problem: there were calls pointing to the address $FC1C but that was in the middle of an instruction. The weird thing, various jumps, branches and instructions pointing to addresses above and under the address $FC1C were OK. Another problem: having the instructions does not mean everything is clear.
So I decided for another solution: I will use the prooven software of the new software for MicroKit09. I have to expand it a bit as it has more keys.
More successors
I thought it was fun to create several successors using other processors. But a remark first: the schematics and the boards have not really been optimalised yet. In general: I kept the original design and replaced just parts. OK, some optimalisation was needed, in some cases I had to swap complete blocks of address and data lines. If I am going to produce a board, then I will have to have a very good look at the design and board again.The boards are listed in alphabetical order. Notice that most boards have more versions. While designing one board, I got an idea which on its turn lead to other ideas and thus other versions. The schematics and boards of all versions are available in links but I decided to show only the latest one the page, just to make the page look less crowded.
Common feature of almost all the newest versions: the original Eurocom-1 has two 6821s on board. I replaced them with other I/O ICs like the 6522, 8155 and 8255, depending on what CPU is on board. In some earlier versions I deleted one I/O IC but in later versions I added it again. But instead of connecting it to a DIN-connector as used on the original Eurocom-1, I connected this I/O IC to a 26-pin header, the same as used on many PC multi-I/O cards. I can connect a 26-pin to 25-pin female D-connector cable and let this port act like a LPT port, or I can connect a 26-oin header to 25-pin male connector and let this port act like a counter LPT port. In the last case I can connect the LPT port of a PC directly to this board using an extension cable. I then can use the PC as an external drive/data source.
- The Eurocom1802
A board based on the CDP1802. - The Eurocom6502
Several boards based on the 6502. - The Eurocom65816
A boards based on the 658516. - The Eurocom8052
A board based on the . - The Eurocom80552
A board based on the . - The Eurocom8085
A board based on the Intel 8085. - The EurocomSC/MP
A board based on the National Semiconductor INS8060B, also known as SC/MP. - The EurocomTMS7000
A board based on the TMS700C02. - The EurocomZ80
A board based on the Zilog Z80.
The software
As I have no idea if I will build the boards yet, so I haven't even started about thinking about the software. And that does include the equations for the GALs. For the SC/MP and 8052/08552 I would also have to build my own assembler and disassembler for them.The EurocomZ80 or possible other versions
I have quite immediatly thought about a Z80 version but in the end I decided against that one. Reason: I have the MicroProfessor-1B and 1P and those two forfill my needs already. And also there are enough other Z80 SBC boards around already.Remark regarding the 6502 version: I completey forgot about the Elektor Junior that I have. But it was at least a quick and interesting exercise.
The processor that then also came to my mind was the TMS7000 and derivates. But I have no experience with them at all. But friends have and we'll see what will happen in the future.
You can email me here.