While I still need to put RTC + Banked RAM circuit to the more permanent prototyping board (currently on a breadboard), I am already thinking about next step - a user I/O for my system, so it becomes a fully self contained system without the need of a PC host.
I recently re-discovered Parallax Propeller chip and it seems to be a very good candidate for this application.
With 8 independent cores (called cogs in Parallax documentation), fast 32-bit architecture and built in video generating capabilities, it should make the task not too difficult.
I already had a QuickStart board from Parallax, which is a starter/demo board for showing of Parallax Propeller (P8X32A) chip capabilities.
The board is equipped with a header providing access to all GPIO pins. I purchased a Human Interface Board/shield for QuickStart that has VGA port, PS/2 keyboard/mouse ports and other features and started experimenting.
First I interfaced my retro keyboard controller to it. You may read about my TI99/4A keyboard controller in my earlier blog updates (titled: "I2C keyboard controller"), although I simplified the firmware as I didn't need I2C support in this particular application. Now it is a much simpler serial keyboard similar to PS/2 but it is not a PS/2 compatible protocol, just voltage levels and pins are PS/2-like. The driver for Propeller chip was easy to implement and this experiment was a success. I could use PS/2 interface on Human Interface board to hook my keyboard up to the Propeller.
Next I went a step further and created a character terminal application out of this setup.
I since switched to Propeller Project Board USB with my terminal application, after adding VGA, keyboard and serial port sockets to it. The software remains the same.
When I add mass storage capability (micro-SD card) to the application, I shall have a fully standalone computer system that will not need a host PC to upload software. The software will be transferred via files on micro-SD card.
On the pictures below my first experiments with composite video and making my keyboard controller talk to Parallax board:
This screenshot shows working character terminal with video generated by Parallax Propeller on VGA display. On the bottom an experimental code of terminal menu, which I will use to invoke various special functions, like terminal setup or access to mass storage:
The character terminal application on Parallax Project board:
I will publish the software for Parallax Propeller once it is finished.
11/21/2016
M.K.
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