robosnacks / z80pio

Learning the Z80 PIO

8255 ports

• Port A @ 04H
• Port B @ 05H
• Port C @ 06H
• Ctrl @ 07H

Outputting 80H to Ctrl sets all ports to ouput
Port A is connected to LCD data pins 7-14
The 4 LSB's of Port B are connected to the 4 LEDS.
The 3 MSB's of Port C are connected to LCD pins 3-6
i.e. bit 7 = E, bit 6 = R/W, bit 5 = RS

LCD pins

Pin1 (VSS): Ground pin of the LCD module. (0V is given to this pin.)
Pin2 (VDD): Power to LCD module (+5V supply is given to this pin.)
Pin3 (VEE): Contrast adjustment pin. This is done by connecting the ends of a 10K potentiometer to +5V and ground and then connecting the slider pin to the VEE pin. The normal setting is between 0.4V and 0.9V.
Pin4 (RS): RS = 1 = data register, RS = 0 = command register
Pin5 (R/W): R/W = 1 = read mode, R/W = 0 = write mode
Pin6 (E): high/low pulse enables LCD module
Pin7 (DB0) to Pin14 (DB7): The data pins.
Pin15(LED+): Anode of the back-light LED.
Pin16(LED-): Cathode of the back-light LED.

0x01 Clear the display screen
0x06 Shift the cursor right
0x0C Display on, cursor off
0x0E Display on, cursor blinking
0x80 Force the cursor to the beginning of the 1st line
0xC0 Force the cursor to the beginning of the 2nd line
0x10 Shift cursor position to the left
0x14 Shift cursor position to the right
0x18 Shift entire display to the left
0x1C Shift entire display to the right
0x38 2 lines, 5×8 matrix, 8-bit mode
0x28 2 lines, 5×8 matrix, 4-bit mode
0x30 1 line, 8-bit mode

0x20 1 line, 4-bit mode