- 6MHz Z80 processor
- 32K of ROM, from $0000 to $7FFF
- 32K of RAM, from $8000 to $FFFF
- Z80 SIO (DART) controlling a full RS-232 serial port (57600 baud)
- Z80 PIO controlling two channels, one connected through a darlington transistor array
- Z80 CTC with four software-programmable timer/counter circuits
- Modified NASCOM BASIC (Microsoft BASIC) interpreter
- Z80 pin header
- Open-source hardware!
Ideas for the future:
- CP/M capability (I’ll need to research CP/M more)
- An additional serial channel (coming soon!)
- An external keyboard/video board to allow standalone functionality
- A memory expansion board
- An expansion bus separate from the Z80 breakout pins
- A programming port for the EEPROM for on-board programming(?)
- Better PCB layout (in progress for V2.1)
- Combining the RAM/ROM and I/O decoding chips (easily doable)
- A version that supports 74HC chips that could (possibly) run off of a battery
- A board that supports both LS and HC chips?
- Potentially fixed in V2.1
- Perhaps a better power connector and supply regulation
My Z80 SBC is designed around hardware that would have been available during the 1980s, with only a few exceptions. Despite this, however, all of the hardware to create the SBC is still manufactured and readily available, including the entire Z80 family and the 74LS family. Every part can be found on Digi-Key, except for the Z80 PIO and the SIO/0 (DART), which can both be found on Mouser. They can be expensive, so I have found that eBay is a good option to find chips for lower prices.
Important hardware info:
Note that the power input for the board is 5V only and is not regulated on the board. Anything higher than 5.5V will damage or destroy some ICs! I choose to use a cable such as this one so that I can use a USB port or AC adapter as a power source.
The Z80 DART is a version of the Z80 SIO with all synchronous functions dropped. It is hardly manufactured (although still active) and a CMOS version was never created. For this reason, it may be desirable to substitute the DART for a Z80 SIO/0. This chip is still produced in its CMOS variant and is nearly pin compatible with the DART. The difference between the chips is that the SIO/0 has pins 11 and 29 as SYNCA and SYNCB for synchronous operation, while the DART uses them for RIA and RIB (ring indicators for modem control). These pins are grounded on the SBC, so either the DART or SIO/0 will work just fine.
I have taken the time to create and layout both a schematic and PCB for this project, and they can be viewed in the project gallery and interacted with at my EasyEDA page here. I currently don't sell PCBs for the board, but you can have them ordered through JLCPCB or any other fabrication service. I may decide to sell boards on a Tindie page if anyone wants me to.