Interrupts. Lovely interrupts. The Z80 has a maskable interrupt, and a non maskable interrupt. The maskable ones having the feature that they can be disabled and enabled from within code. For me, I wanted to implement maskable Mode 2 Interrupts.
Mode 2 interrupts are very powerful. They allow an external device to make the Z80 jump to one of 128 possible locations, by putting the lower half of a 16-bit address on the data bus. this is combined with the contents of the I register to form a location in memory, which should contain the location of the exception handler routine.…
My Teensy Z80 Homebrew Computer A few months ago, I bid on several ‘box of surplus electronic components’ listings on ebay. My lab needed some more components and I saw some of the things I needed in the listing pictures, so thought I’d go for it. I won all of them, at pretty much my lowest bid price, and when I got the boxes was really happy (I paid ~£20 for >£200 of components, most sealed new). At the bottom of one box was a Zilog Z80 CPU, in 40-pin DIP. It’s a Z84C0008PEC, designed to run at 8MHz. It looked pristine, but was not sealed, and it sat in my junk box for quite some time.…
Any PCB Ive designed has been single sided due to my simple PCB etch process. Ive been using KiCad for schematic designs and decided to try to take a design from schematic through to full PCB layout. KiCad has certainly got a fair share of UI issues, but for me it seems to be holding up for what I need from it – until I needed to put a bridge (or link, whatever you call them) on the board layout. Of course a bridgeless layout is always what you strive for, but I expected there to be an easy way to put them into the design.…
This is part 4 of the Pi On The Wall build log, concerning modifications to the enclosure and how everything comes together into its final form factor. Part 3 was about power consumption, and optimizing it for low-power and ultimately low-temperature running. Previous parts can be found at Part 2 and Part 1.
The choice to use a standard (for the UK, anyway) footprint for the Pi On The Wall was made very early on. Ease of mounting to the wall (compatibility with existing wall-fixtures) and a wide range of cheap thermostats to choose from for simply utilising their outer shell.…
