The watch is pretty standard as far as 6502 hardware goes:

  • 65c02 running @ 8MHz
  • 65c22 (controls LCD, keyboard, and buttons)
  • Nokia 5110 LCD (84x48)
  • 32k SRAM
  • 16k ROM
  • C64 Keyboard Connector

Probably the strangest bit there is the full size C64 keyboard connector along the top of the watch. I had wanted to have some form of keyboard input, but most options are entirely out of reach of the poor 6502. The only way i could come up with is to use a preexisting matrix keyboard; I happened to have a lot of unused commodore keyboards, so that's what ended up on there.

The part that ties everything together is really the tiny Nokia LCD. It's interfaced through SPI, which i had to bitbang through the 6522 VIA. The VIA also interfaces with the keyboard, and the face buttons. An interesting thing to note here is that the VIA only has 16 i/o pins, which in this case are all needed to interface just with the keyboard alone. I was able to use some of those pins for both the keyboard and the LCD without causing any sort of corruption with a bit of luck, and a lot more trial and error.


The watch has a few different things on its ROM. The primary thing is G'Mon, a machine monitor i wrote for the 6502. It  supports viewing memory in single and batch, depositing memory in single or batch, jumping to programs, filling blocks of memory with a pattern byte, and moving blocks of memory. I had to strip a few of the less useful commands out in order to fit it on the ROM with everything else. The secondary thing on there is Lee Davidson's Enhanced Basic. I was just barely able to fit into the ROM with everything else, like there are only around 100 bytes free. EhBasic has been modified to hook into the watch's main code, but other than that it's a completely normal version of EhBasic!

The thing that greets you when you start up the watch is the watch interface. Clever name, i know. It just provides a graphical menu you can move through to select what you want to run. This is the only place where the face buttons are actually used, at least on purpose. The topmost button is what brings up the menu. Interesting bit about that: its connected directly to the NMI pin on the 6502, so it can be used to get back to the watch menu from almost anywhere on the thing (unless you crash the 6502).

In my sources, there is a big blob of code that handles interfacing with the watch hardware; It's called the kernel there, but its less of a kernel and more of a library everything else references. Some of the more interesting things in there are the SPI bitbanging stuff for the LCD, and the matrix scanning and decoding routine for the keyboard.

Speaking of sources, they are all uploaded on here, of course. All the assembler code is written to be assembled using KickAssembler, and makes quite heavy use of its macro capabilities, so i doubt it would be fun to try and assemble with anything else. Here i have also included the EhBasic sources that i have modified; They have been modified to be assembled with KickAssembler. Everything builds at the same time, just run the ./Compile.sh script and it will spit out a ROM image. If for some reason you feel the need to fiddle with it, then make sure to go to Configuration.asm: That's the header that holds a bunch of the miscellaneous variables, like the location of the ROM in memory.

If you every wanted to run the software yourself, then you can do that as well. If you set the Emulated variable in the config file to true, then it will build a ROM for use with Symon.

Other Software Toys

I have written a few extra programs to show what the hardware itself can do. The first thing is a little sprite demo that has 8 animated software sprites bouncing around the screen, plus a text scroller along the top. The visibility is quite poor with it, as the LCD sure does take its time with updating the pixels, which causes everything moving to be a little blurry. To combat this I had to wait a bit after each frame for the LCD to...

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