Update Sept 2022

Some recent modifications and additions

Hardware

2 more 65C22 VIA chips to give a total of 3 VIAs providing six 8-bit I/O ports.
- VIA #1 ($6001) : Port A = Keypad
- VIA #1 ($6000) : Port B = LCD_1 (4×20 in 4-bit mode)
  - VIA #1 : IRQ connection to CPU for keypad and CB1 & CB2 buttons
  - VIA #1 Port B handshaking CB1 and CB2 connected to debounced buttons for user input experiments
- VIA #2 ($5001) : Port A = Spare
- VIA #2 ($5000) : Port B = SPI (bit0,1,2,6), Piezo Sounder (bit7)
  - VIA #2 : T1 Timer = square wave generator for sounder using Port B bit7
- VIA #3 ($4801) : Port A = LCD_2 (2×16 in 4-bit mode)
- VIA #3 ($4800) : Port B = Spare
  - VIA #3 : T1 Timer = System Clock Ticks at 10ms rate via NMI connection to CPU
main LCD changed to a 4 line by 20 character display
2nd LCD (2 x 16) added on VIA #3 Port A
LED indicator plug-in boards made to give easy visual indication of VIA output port state
Piezo sounder connected to VIA #2 Port B, bit 7
SPI interfacing using VIA #2 Port B
Buttons for controlling interrupt driven events, each de-bounced with a 555 monostable
555 timer as a power-on CPU reset

ROM Monitor code extended to support the new hardware.

SPI transceive to communicate with a basic SPI slave running on a PyBoard
LCD #2 display of either “Mission Time” or SPI TX/RX data to/from PyBoard
code to send audible beeps of different pitch/duration (controlled by the 2 buttons)
keypad - confirmation keypress beeps
Byte (binary) to ASCII decimal conversion to show 16-bit/2-byte binary data as a human readable decimal number
Use of FLAGS to control background tasks extended/explored

add Serial Interface using Rockwell 65C51 ACIA and MAX232
learn how to code for interacting via serial interface
connect to a Wyse-185 Serial Terminal
[✓ John Pumford-Green, 2022-09-26]~~add DS1306 RTC via SPI~~
[✓ John Pumford-Green, 2022-09-26]~~move system clock back to VIA_1 using IRQ interrupt~~
[✓ John Pumford-Green, 2022-09-26]~~move beep to VIA_3 port B7~~
[✓ John Pumford-Green, 2022-09-26]~~move SPI interface to VIA_3 port B, for future connection to DS1306 RTC~~
- this will leave :
  - VIA_2 ports A & B free for external use
  - VIA_3 Port A = LCD2
  - VIA_3 Port B = Beep and SPI/RTC

— John Pumford-Green 17/09/22 11:50