eda

I've been tinkering with some simple PCB layout jobs in KiCAD over the last couple of weeks. (Hopefully they'll be worth posting here if I can get them finished!) One of these boards is probably going to be cut out on a PCB mill, so it's not going to have a solder mask or silk screen. I wanted to still have the Open Source Hardware logo, there's a big selection available at http://oshwlogo.com/ including downloadable modules for KiCAD but they're all silk screen logos, so I went about creating a copper only logo.

You may have noticed in the schematics I post for various projects that I use KiCAD for all my designs. It's a free and open source package with no limitations on part count, pin count or board size. The software is cross platform, supporting Linux, Mac and Windows, and on Linux you'll probably find it in your distribution's repositories. Unlike the other big open source electronics design software gEDA it is fairly intuitive and not that different from other commerical packages I've used (OrCAD or Altium Designer). Unlike cost free versions of proprietary software like Eagle there are no reasonable limits on the board size, part count or pin count that you can create with this software and while it lacks some advanced features such as more complex curved pad shapes etc. it is very stable now and is well up to commercial work.

The Mark 2 Z80 project featured a pair of memory slots each capable of taking up to 32K of RAM. This meant that a full 64K of RAM could be used because the ROM image is copied from the PIC's memory at boot time. However that didn't seem like much to me so a banking system and MMU were in order. (Also I found I couldn't get the 32K RAMTRON FM1808 chips in DIP any more!)

I recently received an enquiry about how the I/O throttling on the PIC worked to ensure that the PSP was shifting valid data out to the Z80. I had a look back at my code and figured out how I'd done it. However I realised in that conversation that the schematics for the project were vastly out of date and it seemed that I hadn't been keeping as up to date as I thought I was with my local copies.