New Stuff For Old Stuff :: Blog

W hen I first learned about the Orton 3C and its very clever serial routine which toggles A15 (meaning that the max 32k of ram appears twice in the address space) I've wanted to repurpose this for driving a beeper speaker, just as you might have done with the early PETs*  I'm writing this post after successfully playing a tune. The video is embedded near the end of this blog post if you'd like to skip straight to that. Yes, it certainly would be possible to toggle a pin on the digital i/o by 'out'ing to port zero. This would potentially allow for 'bit-banging' multiple voices, with a lot more work than I've put in so far. However, what I love about the Orton 3C is the 'bare bones'ness of it. The whole point is that it can work using only three chips and to that end I've unplugged my digital i/o for this. I didn't go to the trouble of removing the port zero protection shim (3C-PO) but its one logic chip isn't being used here since I...

T he Orton 3C is a minimal Z80 computer which can run using only three chips. As Spencer says, the design is "on the border of simplicity and genius". Credit to Karen Orton, who is sadly no longer with us. It literally gets you hands-on with the Z80. Input of a program (or at least some kind of loader or serial program) is achieved 70s-style using switches connected to the address and data lines.  Spencer has taken Karen's design and implemented it using the RC2014 modular form-factor.  I love the bare-metal-ness of it but couldn't really justify buying one. One birthday later and here we are.  Without using a ROM, programs have to be short or you have to settle down for a lot of toggling. You soon feel the limitations of having no input/output - even a game of 'kill the bit' requires the front-panel i/o (which adds to the chip count). My initial programs involved animating those output LEDs. Of course, any RC2014 module will work and so I tried a program t...