PAPaulHoule·Jun 28, 2024
So did the other member of the "trinity", the TRS-80 model I.
My mental picture is that the kind of display controller I'd like to build is about two large breadboards stuffed with 54xx chips. Such a thing is a bit simpler than a minimal CPU but not that much simpler because you need the stuff to interface with memory. I'd probably want to buy an oscilloscope and/or logic analyzer but maybe I could run it slow and use an AVR-8 Arduino to run test sequences.
Almost everybody who builds throwback computers today uses either an FPGA or a microcontroller for the display controller. For instance
https://github.com/fdivitto/FabGL
is a highly flexible controller implemented for the ESP32 which can do tile-based graphics and sprites for games but also emulate an ANSI terminal. This is used in this SBC
https://www.olimex.com/Products/Retro-Com
Read the rest
puters/AgonLight2/o...
which I am going to highly recommend because this machine is compatible with the old Z80 machines but has a real 24 bit mode with 24 bit registers and also performs an order of magnitude better than any Z80 machine did back in the day.
Modern systems usually avoid the unified memory model that was popular back in the day but that also usually held back the performance of the CPU because one way or another the VDC was stealing cycles. The AgonLight board communicates with the display controller through a serial port, for instance.
This thing
http://www.commanderx16.com/
has a memory mapped register for the address in video RAM the CPU wants to read/write and another for the data. The address register will auto-increment when access the data register so you can read or write video RAM at high speed just by repeatedly accessing the data register. The CX-16 uses an FPGA as a display controller
https://github.com/X16Community/x16-docs/blob/master/X16%20R...