The official programmer from Zilog enables flashing and debugging of the eZ80, but at cost of over $100 USD is certainly not a cheap option.

An alternative solution, detailed here, is to use the low cost Raspberry Pi Pico (original V1) to flash your eZ80.

To make a Pi Pico Programmer, we need to do the following:

1. Download the software image required to run on the Raspberry Pi Pico.
2. Flash that software image onto the Raspberry Pi Pico.
3. Wire some of the pins of the Raspberry Pi Pico’s to the ZDI interface of the eZ80 CPU.
4. Connect your PC to the Pi Pico Programmer
5. Open a terminal application, such as ExtraPuTTY, on your PC and connect to your Pico Pi Programmer over USB
6. Power up your eZ80 Module
7. Instruct the Pi Pico Programmer to flash an image onto eZ80.

Downloading

There are 2 downloads available. tagged Releases and general releases. The tagged releases will have more testing conducted compared to the general releases

• Tagged Releases Expand the Assets section under the tag release you want and download the main zip file.
• General Releases Click on a build, then under Artifacts select the pi-pico-firmware download.

Updating your Pi Pico

1. Press and hold the BOOTSEL button on the Pi Pico
2. While holding BOOTSEL, plug the USB cable from the Pico into your PC
3. The Pi Pico should appear as a Mass Storage Device on your computer - look for a new drive letter.
4. Copy the programmer.uf2 file to the root of the mounted storage device.
5. After copying, the device should reboot.
6. Confirm you can connect on serial over USB, using your favourite serial terminal application (such as PuTTY). You will need to find the COMx number that the USB has remounted as.

Wiring up

Pi Pico	ZDI Interface
GPIO 15	ZCL
GPIO 14	ZDA
GPIO 16	RESET
GPIO 17	ZDI’s PWR (3V3)
GND *	GND *

* Make sure you have short leads, and that the 2 ground pins are connected to ground pins of the Pi Pico.

The Revisions V1.7 has incorrect silkscreen naming for main signal pins - (TDI -> ZDA and TCK -> ZCL)

When looking at the front of the eZ80 CPU module, the pin layout is as follows:

ZDA	GND
ZCK	GND
RESET	3V3

You can use the images below, and follow the colours the ensure you have correct wiring:

Yellow - ZDA - GPIO 14	Orange - GND
Green - ZCK - GPIO 15	Red - GND
Blue - RESET - GPIO 16	Brown - 3V3 - GPIO 17

Flashing your eZ80 CPU

1. Plug a USB cable between your Pi Pico Programmer and your main PC.
2. If using windows, identify the mounted COMx port (use Device Manager). For linux look for the /dev/tty device.
3. Using your favourite terminal program (such as PuTTY), connect to your Pi Pico Programmer You should see a message like:

ZDI Connection ......:    (PWR: FAIL, RST: FAIL, ZDA: FAIL, ZCL: FAIL)

4. Power on your eZ80's RC2014/RCBus backplane.
You should now see a message like:

ZDI Connection OK:  (PWR: OK, RST: OK, ZDA: OK, ZCL: OK)
eZ80 Detected:  ID 0007 Rev AAitialisation...
Available Firmware Version: 0.1.2.0 (2024-10-03)
ZDI>

5. Enter the command FLASH
6. Your Pi Pico Programmer should have reported a completed flash of your eZ80.
7. If you have RomWBW installed on an external memory module, you should now be able to start your retro computer.
   Enter REBOOT to start it.

To see your retro computer, you will need to have the UART serial connection of the Interface Module connected to a terminal application.

Operating instructions

Within your serial connection to the Pi Pico Programmer, you can issue a number of commands.

help Will show the list of commands available

The current implemented commands are:

Commands:

help or h
  Display this help message

status or s
  Display the ZDI status register (ZDI_STAT)

flash [upload]
  Flash the eZ80 with a new firmware image
  default loads the firmware stored on Pi Pico
  upload: expects an intel hex file to be streamed over stdin

verify [upload]
  Read the current firmware version image
  and compare to verify correctness
  upload: expects an intel hex file to be streamed over stdin

break or b
  break the ez80

continue or c
  continue the ez80

reset
  reset the ez80 (internal only reset line is not triggered)

mode or m [ADL|Z80]
  Set the CPU mode to ADL or Z80

led [on|off]
  Configure PC0 as output and turn led on or off

rd or read [ADDR]
  Read bytes from memory

str [ADDR]
  Read a null terminated string from memory

reboot
  Reset and restart the eZ80 firmware

Disclaimer

Please note that this is a kit, produced by a non-expert (me) for hackers, DIYers’ and retro lovers, to tinker with. Please exercise caution and follow good safety practices. You will be working with sharp knives, a hot soldering iron, and small metal components. Be mindful of the risks involved in the build process. I will do my best to answer any questions you may have.

This kit is provided as-is, with no guarantees or warranties. By assembling and using this kit, you acknowledge that you do so at your own risk.