Misc projectsProjects

Z80 SBC – MBC2 and uTerm

uTerm

Today I have started a little DIY project to build a Single Board Computer (SBC) on the basis of a Zilog Z80 CPU.

SBC Projects

You will find various SBC projects, searching the web. Besides Z80 based solutions, various other CPU, e.g. MOS 6502 or Motorola 6809 can be found. All are 8 Bit CPUs.

A superb overview can be found on the website of Mr. Grant Searle, e.g.:

Those designs were successfully implemented on breadboards by Mr. Searle - but after some web search you will also find real PCB designs, e.g. at EasyEDA:

https://easyeda.com/phcreery/Grant_Searle_56K_Z80-U3ZTN5Zhy

https://easyeda.com/Herman/Grant_Searle_56K_Z80-U3ZTN5Zhy

https://easyeda.com/calamari13/Grant_Searle_56K_Z80-U3ZTN5Zhy

https://easyeda.com/Herman/Grant_Searle_6502_SBC-YPpnljgYa

https://easyeda.com/Herman/Grant_Searle_CPM_System-4rpLJZaYk

Hackaday.io

To make the start a bit easier, I ended up at HACKADAYA.IO  and used a published project with name Z80-MBC2 of the User Just4Fun. An excellent project description can be found here. You can also download all required documents, like Layouts, Gerber, Software, etc. there.

To make it even easier, there is somebody in Italy, selling the PCB and required components as a kit. It is the shop of McJohn S.r.l. The complete Kit of the MBC2 as DIY project can be sourced for approx. EUR 60,- (plus taxes and shipping).

Matching the MBC2, there is also a terminal PCB available, called uTerm, providing interfaces for a PS/2 keyboard, a VGA monitor, and a transparent serial interface towards the MBC2. The power supply for the MBC2 is also part of the uTerm.

The uTerm-Design is also a HACKADAY.IO project of user Just4Fun and the Kit itself is also available for approx. EUR 45,- (plus taxes and shipping) at the shop of McJohn.

I ordered both kits for in total EUR 120,- and they arrived just 4 days later. Last weekend, I have started the build.

Building the uTerm PCB

I have started with the uTerm PCB, because it is providing also the power supply for the Z80 board, besides interfaces for keyboard and monitor. The delivered kit was of high quality and well sorted and packed.

uTerm Kit
uTerm Kit

I have started with the flat components, like resistors, diodes and ceramic capacitors. After that I worked „upwards“ - at the end I soldered the PS/2 and VGA jacks, as well as the heatsink for the 5V regulator.

The whole stuff took me about 2 hours and was not that difficult. Only the spacing of the transistor leads was a bit tight, but worked out well.

The primary power supply is a 9V „wall wart“ with at least 1A. A first test looked quite Ok: the green power LED was lightening up. Before I will insert the 74HCT00 chip into its socket, I will do some more measurements, to be on the safe side. The remaining functional tests (keyboard and monitor) will follow, once the Z80 PCB is ready.

The STM32 MCU on the uTerm PCB was already soldered and programmed, using the kit of McJohn. If you source the components yourself, you should be able to solder SMD parts and program the chip. By sourcing the stuff as a kit, I got along with this.

The next blog post will continue with building the MBC2 PCB and the test of the completed system.

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