SmallZ80 Review


This review was posted on the RetroBrew Website this morning by Mr. Wayne Warthen.  I sent him the prototype Rev E0 CPU and Rev B0 Floppy+2S PCBs with the intent that he would build, test, and submit the review.  His input was instrumental in the development of the production design.

I know I mentioned this system here previously, but thought I would provide a little more detail having recently built a pre-production version of the system.

Terry Gulczynski is getting ready to produce a run of these kits, so if you are interested, you should contact him.  His email address is

The SmallZ80 is a compact and full-featured Z80 system with excellent performance and reliability.  It is comprised of a relatively small main CPU board (~5"x6.5") and an optional expansion board (~3"x4").  Construction is straightforward with all through-hole components (there are a couple of small SOIC
chips on the expansion board that come pre-soldered.)

The main CPU board features:
- Z80 CPU (dual-speed, dynamically switchable)
- 544K SRAM (32K fixed & 512K banked)
- Real-time Clock w/ battery
- IDE Interface (supports primary and slave devices)
- 2 Serial Ports
- LED connections for power, drive activity, and disgnostics (3)

The optional expansion board adds the following features:
- Dual drive floppy interface
- Two serial ports, -or-
- Ethernet LAN interface for terminal and printer

Completing the system requires only adding a +5V power source, floppy drive(s) (optional), and a case.

A very complete software implementation is included.  The ROM firmware manages booting and provides system configuration, testing, and monitor functionality.

A CF Card image is provided which implements an enhanced version of ZCPR 3.3 and a very complete set of system tools.   I had no trouble running a variety of standard CP/M applications such as WordStar.

Performance is the best I have seen for a Z80-based system.  The system runs reliably at the maximum Z80 CPU clock speed of 20MHz.  There are no added wait states for I/O or memory.  Additionally, the serial ports are rated for operation up to 230,400 baud, but I am running mine reliably at 460,800 baud (close to 0.5mbps).

The IDE interface on the system is ideally suited for use with Compact Flash cards.  A small CF adapter is installed that allows 1 or 2 CompactFlash cards to be used.  Access speeds are very fast.

The Ethernet interface on the expansion board is probably my favorite feature. After powering on the system, you can simply connect to it via any Telnet-type terminal software.  The Ethernet interface on the board runs at 921,600 baud and provides extremely fast terminal speeds.  The same Ethernet interface can also be used to print to a LAN connected printer.

If you like the retro feel of floppy drives, they are easily connected via the expansion board.  You can use a standard PC-type floppy cable with a twist to install up to 2 3.5" drives.

Complete documentation is included and thoroughly covers assembly, operation, and technical details of the system including schematics.  The documentation is freely available on Terry's website at

Overall, the SmallZ80 provides a system with excellent performance, reliability, and functionality for a great price and small package.  The system has a very professional feel to it for a kit of this type and cost.

Terry has posted pricing for both boards on his website.  All parts are included, but not a case or shipping.  Definitely what I would call "hobbyist friendly" pricing.
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