In this post I’m going to show what has been done in the project.
First of all, an extension board for DE1, that contains a socket for 6502 CPU, was made. I used a toner transfer method to make a PCB. The board connects straight to GPIO0 header on DE1 board:
CPU doesn’t require all pins of the header, so the rest ones have a connectors on the extension board for future use.
AGAT-7 video controller was made in FPGA with VHDL. Now it can to display all video modes of the computer. It uses a VGA output in 1024 x 728 x 65Hz mode for this purpose. Early AGAT-7 versions didn’t use luminance bit, so it was able to display only 8 colours. For compatability with all versions it is possible to turn on/off this bit (by the switch on DE1 board), so the controller can display 8 or 16 colours.
On the screenshots are tests of all AGAT-7 modes:
All ROMs are located in FPGA as well. It includes two char layouts, system monitor and floppy-drive controller program.
All of 96Kbytes of RAM are allocated on SRAM chip on DE1 board.
I2S encoder on DE1 board is used for type in/out, but I’m going to use an original schematic in the final version.
PS/2 keyboard is connected to DE1 and works as AGAT-7 keyboard. It is impossible to connect original keyboard yet.
Audio output was made on a breadboard using modified original schematic.
140K floppy drive was made on a breadboard as well. Now it can read “nib” disk images from a FAT (16 or 32) formatted SD card. An image can be chose on 20х4 LCD display. Directories are supported. There is no support of long file names, to save a microcontroller memory. Also, it is inconvenient to work with long file names on a small LCD. Another limitation is not more than 80 files in a direcory. Dispite that I believe that it is enough (a collection of images can be splitted between directories), I’m going to increase this amount in the next version on STM32L microcontroller (it has twice more RAM). Write mode to an image hasn’t been done yet:
RAM test has been launched from my “floppy-drive”:
And here are screenshots of OS “RAPIRA” and “SCHOL’NICA” which were successfully loaded from my “floppy-drive” as well:
Games are also can be launched 😎 :
My next steps are:
- Make 840К “floppy-drive” as well (STM32L microcontroller will be used).
- Move existing 140K “floppy-drive” from ATMega64 to STM32L and add a write mode.
- Build tape in/out on a breadboard and test it.
- Make a full schematic of the project in KiCAD.
- Make Rev.0 of a PCB with all elements of the computer except serial-parallel interface and extension slot, but with accessable pins of FPGA chip and CPU for debugging and developing the rest of the computer.
- Create Rev.A of PCB with all planned devices and slots on it. It can be used for a DIY kit as well if there will be some interest to it.
That’s it. Hope you like it. Please live your comments and subscribe to RSS updates. See ya!