Zeta

Project Zero : The RAM In continuation of the development of Project Zeta, the small compact Z80 based microcomputer that I am slowly learning on, comes the next installment.. The RAM board! Now this is actually performing double duty as the ROM as well, as the inital plan is to program the RAM at boot with the program that the system is to be executed. Design The RAM board is designed to provide a nice simple breakout for two 32k SRAM IC’s onto the memory bus for the Z80, nothing fancy here, no bank switching or real logic. We utilize two logic gates (7432 OR gates) to decode the output gating and the write enable on the two chips. Along with an inverter on the A16 line of a single transistor. ...

Project Zero : The MCU (Programmer) To begin the design and creation of the project I worked on the base board of the design.. The Microcontroller, an Atmega 2560 was chosen to form the programmer and interface to the whole system primarily because of its large pin count and also I happened to have a few left over from a previous project. The Atmega is configured to run from its internal 8Mhz oscillator and to also output this out the CLKOUT pin so that later on this can be used to provide the system clock to the Z80, this is switched with a GPIO that can be used for single stepping support via a 74AC157 Logic gate. Almost all of the connections on the Atmega are used for the CPU bus and associated lines, this ties up 34 pins of GPIO on the Atmega. The Address bus and data bus are arranged such that they fall neatly on the ports of the atmega so that we can directly write bytes to the ports directly without any bit fiddling. ...

I have been following Veronica, a 6502 based computer being built by Quinn Dunki over at Blondihacks since the projects beginning in late 2011. Recently when sorting through my stock of collected parts I realized had almost all of the the required parts on hand. Whenever people talk about what they learned to program on it tends to come back to a few main chips, namely the 6502,z80 and the 6800. The z80 took my interest, partly because I liked the challenge of having less information and compilers to rely on, partly because I liked the IO input/output system it used but mostly purely because I had one that I believed worked. ...