Table of Contents
2650 Max v1
Introduction
Welcome to my build of Michael Cvetanovski 's 2650 Max SBC.
More information here:
https://sites.google.com/site/gogleoops/2650-max
Micheal has some other interesting projects on his OLD Micros site as well, check it out:
https://sites.google.com/site/gogleoops/
This build was inspired by my very first computer an Electronics Australia 2650 system.
https://archive.org/stream/EA1978/EA%201978-05%20May#page/n57/mode/2up
I don't have that system anymore but still have the CPU, PROM and transformer. The CPU will be using in this build - nearly 40 years old now.
Read all about an awesome remake of this system I just stumbled upon:
http://www.postincrement.net/2650-remake-finished-and-working/
Features
- 1Mhz 2650 CPU.
- NVRAM chip used for RAM and ROM storage. The ROM area is “write protected” by the GAL logic.
- PIPBUG monitor available.
- MWBASIC monitor available.
- TTL level 300 baud direct interface to pipbug monitor and mwbasic.
- Three 8 bit input/output ports.
- TTL level serial port.
Pictures
Parts List
| Item | Qty | Description |
|---|---|---|
| 2650, 8255 socket, | 2 | 40pin DIP socket |
| DS1245A socket | 1 | 32pin DIP socket |
| PAL socket | 1 | 24pin narrow DIP socket |
| MC68B50 socket | 1 | 24pin DIP socket |
| IC1 | 1 | Signetics 2650 microcomputer |
| IC2 | 1 | i8255 PPI (programmable peripheral interface) |
| IC3 | 1 | Maxim DS1245Y-70 128Kb non-volatile memory |
| IC4 | 1 | GAL22V10 (preprogrammed) |
| IC5 | 1 | MC68B50 ACIA |
| IC6 | 1 | SN74LS14N hex inverter with schmitt trigger |
| Y2 | 1 | 1Mhz DIP14 5V active crystal oscillator |
| Y3 | 1 | 1.8432Mhz DIP14 5V active crystal oscillator |
| R1, R2, R4, R6, R7, R8 | 6 | 4K7 resistor |
| R5 | 1 | 47R resistor |
| R9 | 1 | Current limit resistor 1K8, 2K2 etc |
| C1 | 1 | 47uF tantalum capacitor |
| C2, C3, C4, C5, C6, C7, C9, C10 | 8 | 0.1uF ceramic capacitors 2.54mm |
| D1 | 1 | 3mm LED |
| Reset | 1 | PCB mount push button |
| PortA, PortB, PortC, invgates | 4 | 2x5pin male pin header 2.54mm |
| Comms, A15, A16, E | 4 | 3 pin male header 2.54mm |
| H1, Ucomms | 2 | 4 pin male header 2.54mm |
Assembly Instructions
If you have a complete set of parts, here's a suggested assembly guide
- All IC sockets
- Resistor R5
- Resistor R9
- All other resistors.
- 3mm LED - polarity important
- Reset SW1
- All 0.1uF capacitors
- Capacitor C1 - polarity important
- Crystal Y2, Y3
- Bend up pin 2 of SN74LS14N up solder in.
- All 2x5pin headers
- All 3pin and 4pin headers
- Power / reset connector
- Populate all IC sockets.
I found using a dab of superglue on the pin headers helped keep them in place for soldering. I also recommend using gold plated pin headers as the un-plated ones solder poorly and leave a unsatisfactory finish.
If you are using the v1 PCB as I am there are four modifications to be made which are documented on the designers site, see link above.
Resources
2650 Microcomputer
RS232 level logic circuits for the 68B50
Assembly Instructions
If you have a complete set of parts, here's a suggested assembly guide
- All IC sockets
- Resistor R5
- Resistor R9
- All other resistors.
- 3mm LED - polarity important
- Reset SW1
- All 0.1uF capacitors
- Capacitor C1 - polarity important
- Crystal Y2, Y3
- Bend up pin 2 of SN74LS14N up solder in.
- All 2x5pin headers
- All 3pin and 4pin headers
- Power / reset connector
- Populate all IC sockets.
I found using a dab of superglue on the pin headers helped keep them in place for soldering. I also recommend using gold plated pin headers as the un-plated ones solder poorly and leave a unsatisfactory finish.
If you are using the v1 PCB as I am there are four modifications to be made which are documented on the designers site, see link above.
Resources
2650 Microcomputer
RS232 level logic circuits for the 68B50
Memory Map - 4 x 32Kb blocks
| 0X00000-0X20000 | A15 | A16 | |
| 0X00000 | 0X07FFF | L | L |
| 0X08000 | 0X0FFFF | H | L |
| 0X10000 | 0X17FFF | L | H |
| 0X18000 | 0X20000 | H | H |
