Build Your Own Z80: TESTS I

CPU No Operation (NOP) Test:

 - Used to test Z80 CPU and buses: Address, Data, Control.

 - The data bus is pulled low which effectively causes every data byte read to be "0x00" which is recognized by the CPU as a No Op; it does nothing but increment the Program Counter (PC) which can be seen via the Address Bus LEDs

 - The PC starts at 0 so the first address read by the CPU is 0. The data contained in location 0 is 00. The NOP is executed and the PC is incremented. The net effect is to see the address bus increment up to 65535, if you have LEDs attached to it through current-limiting drivers

ROM Test

EEPROM Test:

 - Determines if the EEPROM, busses, and address decoding logic are working properly

 - A 32KB (256K x 1-bit, 32K x 8-bit) EEPROM is pre-programmed with nothing but 0x00 NOPs

 - 74hct32 and 74hct14 are "glue" logic for decoding the EEPROM as the lower 32KB of the 64KB address space is tested

 - Directions are provided to build an Arduino 5v Nano-based EEPROM programmer

SRAM Test:

 - EEPROM contents are changed from NOPs to a program that will copy a data pattern to every location in the 32KB SRAM

 - The glue logic as well as the upper 32KB of the 64KB address space are tested

 - See the ROM Test above for a link to building the Arduino 5v Nano-based EEPROM programmer

Input/Output Test 1:

 - We'll configure the 8255 PPI (general purpose programmable parallel I/O device) to output to an LED bar graph display

Input/Output Test 2:

- We'll configure the 8255 PPI to accept input from a 4x4 keypad and output each key press position to an LED bar graph

Input/Output Test 3:

- The 8255 will be configured to output a command string to configure a 2x16 8-bit parallel LCD panel, and then output a data string to the LCD

Input/Output Test 4:

 - The 8255 will be configured for simultaneous input and output: user input from a 4x4 keypad is output to a 2x16 LCD panel

CPU Single-Stepping Test:

 - Now that we have our CPU, ROM and RAM working, we can test our new CPU Single-Stepping circuit to watch our assembled code progress instruction by instruction on 7-segment LEDs.