- Port PCB designs to KiCad
- CPU board:
- Memory Board:
- SIO board:
- In progress
- PIO board:
- Not started
- Front Panel:
- Not started
- Backplane 5:
ZTO-80 Modular System Features:
- Custom bus built for the Z80 family and beyond
- Pre-designed backplane, CPU, memory, SIO, PIO, CTC, and other boards
- Nearly infinite potential for customization and expansion
- Built using off-the-shelf parts
- CPU board:
- On-board oscillator with enable jumper
- Reset switch (also on backplane)
- Breakout header for signals not included on bus
- 74HCT data and address buffers allow for either a TTL or CMOS Z80*
- CMOS is recommended for compatibility and because of availability
- *Bus signals not buffered due to board size limitations. I have not tested with a TTL Z80, so use at your own risk.
- Memory board:
- 32K ROM, 32K RAM
ZTO-80 SBC Features:
- 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
- Bus expansion header
- Open-source hardware!
The heart of the ZTO-80 System is the Z80 CPU, first designed by ZiLOG in 1975.
The ZTO-80 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 74xx family. As of writing, every part can be found on Digikey if you use a Z80 SIO/0 in place of the DART. They can be expensive, so I have found that eBay is a good option to find chips for lower prices. However, you do need to be careful about fake and counterfeit chips. Once I create a good BOM I'll add it to the project files, but most of the part numbers are silkscreened onto the board or can be found in the schematics.
Important hardware info:
The term "ZTO-80" can refer to either the SBC or the modular bus design. Usually, to clarify which I am talking about, I'll say either "ZTO-80 SBC," "ZTO-80 Bus," or "ZTO-80 Modular System."
Note that the power input for the SBC is 5V only and is not regulated on the board. Anything higher than 5.5V can damage or destroy some ICs! On the SBC or backplane, power is provided through a 5mm barrel jack with a 2.1mm pin. 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. On the SIO card, either serial port can be used to provide power to the whole system, which is useful as it means that you only need one cable to use a minimal system. It is very important to only connect one power source at a time. I recommend removing the serial power jumpers from any port not being used to receive power so that it is difficult to accidentally connect multiple power sources at once.
The Z80 DART is a version of the Z80 SIO/0 with all synchronous functions dropped. It is hardly manufactured (although still active) and i cannot find any info on a CMOS version, so it was likely 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 my designs, so either the DART or SIO/0 will work just fine. Just be aware of incompatibilities between CMOS and TTL chips, but I've never had any noticeable problems when using a DART.
I have taken the time to create and layout schematics and PCBs for this project. They can be found at the GitHub link on this project page....Read more »