6502 : Screen and Keyboard

 

I am thinking that the 6502 should have its own screen.  Traditionally an RS232 serial monitor would be appropriate for the time.  Back in the day I used a VT100 (text) and Tektronix 4025 (graphics) terminal attached to a PDP11 minicomputer.  I did consider buying a small terminal but, unsurprisingly, they aren’t made anymore.

I have an ESP32 and Waveshare 3.5” LCD screen which could be used.  Commands sent to the ESP32 could then be interpreted and the results displayed on the LCD screen.  Graphics would be done by commands as they were on Tektronix graphics terminals.  This is not similar to home computers which used memory map graphics.   ESP32 may be able to do cycle stealing graphics where it interleaves display and 6502 operations.  This would be aligned to the home computer ethos but quite a complex project.

I then considered how an RPI could be used.  Instead of connecting 6502 serial to the PC running putty we could connect it to my RPI 2B (called PI2)  which has a 3.5” screen attached.  I wasn’t sure how to connect my FTDI cable to the RPI.  I connected up with a loopback wire between RX and TX and then set about working out how to use it. 

Using a normal ssh session on PI2 I tried a utility miniterm (which seems to be python but works for me at the RPI command line) and it gave me a choice of ttyASM0 (console) and ttyUSB0  (serial port).  dmesg also shows ttyUSB0 being attached when I plug in the FTDI.  With miniterm using the serial port characters typed at the keyboard were echoed via the loopback wire.  I then setup miniterm to access the 6502 (miniterm /dev/ttyUSB0 -s 19200.  Rebooting the 6502 shows me output in the miniterm session.

PI2 has a Waveshare 3.5” screen directly connected to GPIO pins.  At installation the screen is configured so it is a console.  When PI2, which runs headless, is turned on boot messages are displayed.  On completion there is an autologin to user pi.  Connecting a USB keyboard to PI2 allows keyboard input at the console.  If I start miniterm at the console I see 6502 output on the LCD screen and can enter commands as 6502 input on the keyboard.  JOB DONE!

This is a brilliant solution, for a few minutes work we have a small self-contained text screen and keyboard for our 6502 system.  Purists will rightly argue that it is a modern powerful SoC acting as a dumb screen for a primitive system.  However a modern dumb terminal would be more expensive and have many components.  An old terminal would be real retro hardware, but we aren’t in that business.

miniterm doesn’t have many features and doesn’t support ANSI escape codes well.  I  tried minicom and putty but they didn’t work well for me but I settled on the linux utility screen which is simple but effective.

I can visit the screen topic later to see whether I can find a bit-map graphics terminal solution but for now I am happy with the system.