Z80 ICE by Tauntek

This Web page produced Jan 27 2009, updated Aug 6 2019. To email me, see see my ordering Web page for my email addresses.

Summary

This is a Web page about Bob Grieb's Z80ICE device from the year 2009. It's a Z80 chip operated by a CPLD programmable logic device, which is controlled by a PIC processor commanded through a serial port. This becomes an "in circuit emulator" or ICE device for debugging Z80 designs and products. In-circuit controllable processor emulators like this, are convenient for debugging vintage-computing hardware and software.

As of 2019 and a few years prior, Bob Grieb does not produce this kit. I do not sell this kit. Here's Bob's tauntek.com Web page about it. Bob is a designer and this is/was an example of his design work. Contact him about the kit, but he will likely tell you "the Web page provides the PC board files and programming if you wish to make the kit yourself" or words to that effect. - Herb Johnson, 2019

Introduction

photo of ICE kit
photo of ICE board, chip side
photo of ICE board, back side
photo of Z80 cable and plug-in adapter

The ICE operates in two modes; "GO" and "QUIT". In "GO" mode the Z80 runs at full speed, and the ICE provides abilities to control breakpoints and interrupts only. In "QUIT" mode, the ICE operates the Z80 to access its registers and the devices and memory the Z80 operates. The ICE operator can examine, modify, load and save memory in "QUIT" mode; entering a "G addr" command, the ICE enters "GO" mode again, until a "Q" command is entered via the ICE serial port.

To test, we've set up a NorthStar Horizon S-100 4MHZ Z80 system, running CP/M 2.2. This operates a Z80-driven hardware floppy disk controller: it will test the ability of the ICE in "GO" mode to allow the Z80 to handle diskette reads and writes successfully. As the Horizon uses a serial terminal at 9600 baud, we've set up a physical serial cable switch, to swap the terminal back and forth between the CP/M system and the ICE debugger.

Here's the ICE plugged into NorthStar Horizon CPU board.
This is the serial cabling switcher, from ICE to CP/M serial port.

By and large, the terminal can be switched successfully between CP/M and ICE. While this did not always work, it may be due to false serial signals sent during switching. More testing will resolve this.

In this photo of the terminal screen, we see ICE "==>" prompts & CP/M "A>" prompts. The photo shows, from the top, the ICE in operation, after CP/M was loaded and running. A hardware reset on the NorthStar brings up the "Z80 ICE V0.62" command, after typing CR's at 9600 baud. The ICE auto-bauds after reset, and for now starts up in "QUIT" mode. A "g" command defaults restart to location 0000. CP/M restarts its operation from that location. Switching the terminal to the CP/M serial port, it shows the CP/M "A>" prompt. "dir" was entered and CP/M displays a directory of the A drive.

This photo is a CP/M memory test, restarted from ICE. At the top, the test says "Walking bit left test", part of the memory test process. The terminal was switched to the ICE and CR was entered, showing the "Err ===> prompt." "Q" mode puts the ICE in control of the Z80 processor and the Northstar hardware. A register dump is shown, followed by a memory dump with the "d 100" command. In CP/M, programs begin at 0100, and one can see some ASCII text of the memory test program. The "g" command restarts the Z80 at the point where "q" was entered: this address is shown by the ICE on the screen. Then the terminal is switched to CP/M again, and "walking bit right test" reveals the CP/M memory test program has continued from where it was stopped.

Copyright © 2009 and 2019Herb Johnson