M847 extended version V1.1 project files
This is a project to add a bootloader or bootstraploader to a Digital / DEC PDP8/e PDP8/m PDP8/f computer.
Originally Digital had an M847 diode bootstrap loader. Because the EPROM was not invented yet, there were 32 x 12 diodes making it a 32 word bootloader. So a -not programmed- board had 384 diodes in the program field. You could write your program by cutting out these diodes.
Quite a lot of work to 'reprogram' such a board.
The M847 extended version does not have a 32 word limit. So much bigger programs can be loaded. The idea is to put in as much test programs and bootloaders as possible. The first 15 programs are selectable by the dipswitches on the board. This makes such a program a default program.
After toggeling the SW switch one time, the default will be loaded.
Toggeling more than once shows up the programnumber into the address lights. After a time out of 3 seconds the displayed program will be loaded. If a not existing program is selected, the programnumber stays in the address line after the 3 second time out. Then you can start toggling in the program again.
The initial V1 version puts out a lot of debugging data and is slowed down a lot. This can be tuned up but it does give a nice blinkenlight effect while loading.
The PCB has been made in trough hole components. This because people can built it without any special tools. The ATMEGA328 needs to have an Arduino bootloader in it. You can buy them already flashed but you can program this also with an Arduino as ISP programmer.
The picture "Flash Arduino bootloader.jpg" shows how to connect an Arduino as ISP to flash the arduino bootloader into the Atmega328. I used a 6 pin cable and on the programmer side I took out wire 5. Wire 5 goes to digital pin 10 on the Arduino ISP. You have to do this only once. If you bought an Atmega328 with arduino bootloader in it then there is no need to flash the CPU with the bootloader.
Now you have to put in the "M847 extedned edition Vxx.ino". For this the board needs 5V. The easiest way is to put the board in the PDP, connect a fully wired serial cross cable and powerup the PDP.
In the Arduino IDE you have to select the "Arduino Uno board" and your com port which you want to use on the PC. Then just open the .ino file and press upload. Now you are ready to use the board.
First demo: https://youtu.be/0nqb3zyAv2g Second demo: https://youtu.be/xYt5kZuUb3A
To do: Test in parallel with my real M847 to check if it gives some sort of collisions...
Regards, Roland Huisman
Copyright 2019 Roland Huisman
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