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This because only CMOS version, under given condition that are respected in this schematic, has logical levels compatibles with Atmega32A and 74HC00. Note that only the CMOS version of the Z80 CPU can be used here. The 74HC00 is used as RS flipflop to stop the Z80 CPU during I/O operation, giving the needed time to the Atmega32A to interact with the Z80 bus, and as part of the MMU. Also both SD and RTC modules (if present) must be removed from the board when the ICSP port is in use.Īs clock source for the Z80 CPU it is used the 16MHz Atmega32A oscillator, so the " external 16MHZ osc." bootloader variant must be chosen when flashing the bootloader from the Arduino IDE!. You can use the on board ICSP port J3 (also called ISP port) to write the bootloader, but remember to disconnect any other connector when using it. Inside the Atmega32A it is flashed an Arduino bootloader taken from here, and it is possible to use the Board Manager of the Arduino IDE to "import" it.įlash the Arduino bootloader at first (with the method you prefer), next you can upload the IOS "sketch" (the I/O Subsystem that interacts with the Z80 bus and " virtualizes" the EEPROM and all the peripherals seen by the Z80 CPU) using Arduino IDE.
![download z 80 cpu download z 80 cpu](http://www.z80.info/gfx/nicd-raw.jpg)
The MCU Atmega32A is used as universal I/O subsystem, as Eeprom, and as reset and 4/8MHz clock generator for the Z80 CPU.
![download z 80 cpu download z 80 cpu](http://www.gilesgoat.com/NewSite/images/Z80bigimg01.jpg)
The schematic and the BOM are attached in the Files section. If you want the 16x GPIO expansion (GPE option) add a MCP23017 too. The needed ICs for the "base system" are:
![Download alien trilogy dos](https://cdn1.cdnme.se/5447227/9-3/24_64e61dfd9606ee7f8b257167.png)