UART protocol between front panel board and digital board.
All display and key data transfer between CPU and front panel board is done by UART interface
Captured log example attached.
Display data transfered in ASCII + control bytes for blinking/special segments, etc.
R603,R604 on signal lines was probed with CP2103 USB-UART bridge
Settings: 8N1 9600 baudrate
Easy to use for custom application if perform full decode for protocol.
Requirement for front-panel board and VFD:
- +5.5VAC with center tap for filament
- +60 VDC for segment drive
- +5VDC for controller and logic
- 4MHz clock
- System reset signal line