Z80 Build From Scratch

PAGE 19: PPI LCD LED Testing

Z80 Breadboard Prototype Tested:

The v1.1 Z80 basic system containing CPU, ROM, RAM and UART has been fabbed and is working well. You can see it in the video at the bottom of the page. There were a few wiring errors which will be fixed in v1.2.2.

We will be driving signals across and out of the board to a PCB containing a 82c55A P.P.I. or some other device. As such one-way signals like Addresses and Control lines will be buffered with 74hct541s and the two-way data bus signals will be buffered with a 74hct245.

In addition to the schematics we also have a short video of the PPI being used to drive an LED bar graph at the same time that it outputs a message on the 20 x 4 LCD panel.

Base Z80 System v1.2.2 Schematics

Short Video: v1.1 Base Z80 System Driving a Breadboard Prototype Containing a PPI with LEDs and LCD

These are the schematics for the PPI Expansion board v1.0:

And here is the assembly code to test both the LEDs and LCD panel: PPI_Synced_LED-LCD_Test.asm