EEPROM chips have come in. (CAT28C256)
Now that we have a low frequency adjustable clock source and a single-stepping instruction interface to the Z80 processor we can test EEPROM chips after they have been programmed. Most every EEPROM chip consists of a certain amount of data and address lines as well as control lines for reading, writing, and enabling the chip. The reading and enable control signals are used by the Z80 for data retrieval from the EEPROM. The enable and writing lines are used to program the EEPROM.
There are many DIY EEPROM programmer circuits and solutions scattered across the internet. There are also many EEPROM programming units that you can buy on the market. These units range from over $500 to under $50. Weighing our options I would suggest saving the headache and buying an EEPROM programmer.
Let me be honest though, even buying a universal EEPROM programmer is a pain. I invested in a G540 universal EEPROM programmer. Its quirks include: complaining about not being plugged in to the USB port when it already is, varying levels of confirmation of success within the software, incorrect instructions for chip placement, and just down-right awful manual instructions. None the less it works for my CAT28C256 (32K X 8-bit) EEPROM chips, and at this point I am thankful for at least getting it to that point. You can get a G540 Universal Programmer for around $30 to $50. If I had a better option for a mid-range EEPROM programmer in the $100 range I probably would have paid the extra money and looked for a more user-friendly software environment.
The next tests I will do will be ROM only instructions. I connect the ROM chip to the Z80, and find some instructions that will only require the ROM. I will use my stepping circuits, and adjustable frequency circuits to make note of the address and data bus.