Skip to content

design

85uino

For a while now, I have been working a bit on the background on a little project that I've thought about since I have watched the videos of Anders Nielsen and his 65uino, an arduino sized board with an 6507 (a DIP-28 version of the 6502) as its brain, complete with a 27512 for ROM, even if he just uses a few kB of the IC, and a 6532 for IO, Timer and 128 Bytes of RAM.

Which then made me think. I did have an Intel 8085 and a few support ICs sitting around, unused.

So, why should I not attempt to build something similar? An 85uino. Something with a 8085, a 8155 256 Byte static ram with 2x 8 bit IO Ports, 1x 6 bit IO Port and a 14 bit Counter/Timer, and either a 27128 or a 27256 as memory, which can be set by a jumper port on the bottom.

Which is what I did.

IMG_20250119_130144_611.jpg

I made a little mistake with the header on the right, which should be on the top, but I didn't check, before I was half way through soldering all the pins and then said, eh f* it. And the RAM is a AT29C256 Flash memory IC that I got myself some time ago. Much easier to reprogram quickly.

Well, at least that is what I am out to eventually get working at the very least...

I had to make a few compromises however...

For one, the footprint of the PCB is more along the line of the Arduino Mega, but theoretically it is only actually compatible with normal Arduino Hats. Not with anything that contains analog inputs though. Mostly this is due to the size of the 8085, when compared to the 6507.

But, that PCB size allowed me to indulge a little. For one, the large header that would normally be on the right side of the Arduino Mega, has been sort of retained, as I have turned it into a bus for the system, so its easier to extend it. Secondly, I've added that 'jumper bay' in the lower right, which allows me to set the timer output from the 8155 to any of the Interrupt pins of the 8085.

Like the 65uino, it has an I2C port for a display, though those pins are also shared on a second header. Downside is that other then the 6532, the 8155 can only set the direction of an entire port, so I've made the decision to set certain ports to be inputs, while others are outputs.

The power supply is either through an external barrel jack (missing on the PCB because I don't have any at the moment), but also through an USB Type C port, which is also connected to a CH340C to allow me to leave out any external serial port at the moment. And with the 8085s integrated serial IO, SID and SOD, setting that up is easy. (Spoiler: At the moment the CH340C doesn't seem to work as off the first power on test, no idea why at the moment.)

Since I was going with SMD parts anyway, I decided that I was going to use a few single gate ICs, so that I would not have gates around that I didn't use at all. Been a bit harder to source though, but since I am not doing any hand soldering of SMD parts, not a problem.

DWMC-85-Mini.png Download PDF

So far, I have just gotten the latest variant of the PCB from JLCPCB and completed soldering it. Tests have not yet been done, safe for a power on test, without the big ICs, so see if something popped, which something did. No idea what though, I think it might be the CH340C, but I sill see when I do further tests. A second power on test with all ICs made nothing pop.

Anyway, enjoy a few images from the build process.

IMG_20250119_111502_016.jpg Bare PCB, fresh from JLCPCB

IMG_20250119_111607_207.jpg Preparing for the solder

IMG_20250119_111737_120.jpg Lets get some paste in place

IMG_20250119_111917_866.jpg Freshly pasted PCB

IMG_20250119_112226_528.jpg Preparing to place all the SMD parts with a hopefully steady hand. The booklet is just a sample book with lots of 0805 resistors and capacitors.

IMG_20250119_115206_367.jpg All SMD components in place.

IMG_20250119_115357_228.jpg Preparing to reflow the SMD parts. Fume extractor in the background and the hotplate is a DIY thing. Nominally, it is one that should be able to control the hotplate, but for some reason, the solid state relays doesn't work as expected. Still get a temp reading through, as I'd just directly attached the hotplate to 230V at the moment and control everything through the power switch.

IMG_20250119_122203_252.jpg Reflow finished and ready to install the through hole parts.

IMG_20250119_125625_378.jpg And all the through hole parts installed. With the right pin header on the back because I didn't look at it!!! Argh!

DWMC-16 v2 Design Part 5c: Special Register Simplification

So, I have done some thinking, concerning my decision to add four Index/Offset Registers/Secondary Stack Pointers. And since I want to be able to write a nice, simple version of Forth for the DWMC-16... I decided that I would throw the Special Registers out of memory and put them into the second Register Bank, where I can do a bit more with them, without the need to load and reload them. Largely this is to cut down on commands to load addresses into the Index Registers...