Electronics, coding and hacking. And ADD.

6502 plans revealed


My apologies for not updating the blog as frequently as I once promised to. I'm busy these days as I'm coding a part for a C64 demo, moving to a new house, and taking exams in electronics, in addition to entertaining my wife and kids. So, needless to say, there's not much time to play with the toys. I've been thinking a lot about the 6502 computer, though, and I'm going to let you in on the oh-so-secret plans right away:

CPU and memory: Not surprisingly, it will feature a 6502. More precisely, a Rockwell 6502 CPU accompanied by 32K SRAM and a massive 32K ROM. The ROM will share its address space with the items following.

GPU: I'm planning to do the GPU myself, quite possibly in FPGA, but for now I'll settle with something pre-made. I've ordered a few NOS TMS9928's - old arcade video chips. They have 16K of "internal" RAM and can easily be mapped into the address space without too much hassle, and they also feature multiple screen modes. Yes, even bitmap modes, which make them ideal for my system.

Disk controller and I/O: The disk controller will be performed by an ATmega16 with an SD card interface. That's more than sufficient for this little thing. This controller will also deal with the PS/2 keyboard and RS232 port.

Audio: I'm very inspired by the Micro SwinSID (6581 SID clone), which is based on an overclocked ATmega88. Choosing this approach, and mapping it into the right addresses, I get access to 40K+ SIDs, ready to be played on my system.

Then there's also a CPLD board and programmer on the way from Hong Kong. I think it's time I started learning that stuff, as I've come to the realization that not everything can (or should) be solved using micro controllers. This stuff is reserved for the lazy days, though.

So, those are the plans. Everything will exist in the form of a breadboard project until I get it working just right....

Aiming for the stars.. or satellites..


I'm experiencing an increasing interest in wireless energy and communication, so recently I felt the urge to explore the signals provided from "up there" - satellites. Weather satellites continuously transmit images and weather data via short wave radio. Capturing and decoding a signal is trivial, but the hardware behind it needs a little work.

The satellite NOAA-18 frequents my neighbourhood several times a day, and should be a good candidate for listening. In order to tune in, I need to fix on the 137.9125MHz frequency somehow, for the few minutes it is within my range. The doppler effect also needs to be taken into consideration, but I'll focus on a fixed frequency for now.

Most of the stuff mentioned here are ideas, want-to's, theories and thoughts at the moment, most of which has a very low WAF 1). For example the quadrifilar helicoidal antenna that will decorate our roof top.

If I'm granted the privilege to install all the equipment (which I quite honestly doubt I ever will), the rest is a matter of software development - for example, decoding the satellite image data according to the NOAA APT Frame Format specifications.

And then, who knows, it'd be cool to make a pluggable standalone device with an antenna connector in one end, and a RJ45 (TCP/IP) output in the other, providing live data via an internal web server.

A lot of exciting stuff here, time will show if this will see the day of light or not. But I have my hands on an old satellite receiver already...

1) WAF - Wife Acceptance Factor. Take note of this abbreviation, I'll be using it a lot.

8-bit R2R ladder


As I've mentioned earlier, I'm an active breadboarder. Having nothing to do, and being a while since I did my own R2R ladder (DAC), this day felt like a good day to refresh those ole' skills. Using an ATmega8 (for a change) and a handful of 1K and 2K2 resistors, an 8-bit R2R ladder was born. The ATmega outputted a 256 bytes long sinewave [0..255] on eight pins, connected to this ladder:

8bit R2R DAC schematic

And here it is on the breadboard:

8bit R2R DAC breadboard

The results were pretty nice, too. I cannot complain about the resolution from this unamplified signal:

8bit R2R DAC oscilloscope view

Quite pleased with this one, actually. I'm not implying anything, but this might be the beginning of an audio chip for the infamous 6502 project.

MSP430 + SD card


I'm hooking the MSP430 up to an SD card reader (via a 3.3V logic level shifter, in case you wonder). The software isn't ready yet, but I'm getting there.

MSP430 with SD card

The goal for this project is to test out the MSP430's SPI functionality, as well as dumping a text file from the SD card to the computer, via the micro controllers UART interface.

There's a thought behind the stupidity, it's for the (still undisclosed) 6502 computer project. I'm hoping to eliminate its use of EPROM, replacing it with SRAM fed with firmware from the SD card. That way I don't have to unplug anything when upgrading the "ROM" software - I'll just upload a new image file to the card, and voila. The controller will also serve files to the computer's real RAM, by acting like a disk controller.

Getting to know my MSP430


Got one of these the other day. As an Atmel guy (if you look aside my brief flirt with the Microchip PIC controllers in the beginning), I was curious what the world of TI looked like. A tip led me to the MSP430 Launchpad, and at the cost of $4.30 (+ shipping) I had to get one (I actually bought two)

TI Launchpad

It was surprisingly easy to "switch", everything worked out-of-the-box. No startup problems, everything auto-detected and... well.. worked.

I ported a 4-bit LCD driver from the ATmega8, and it took me about 15 minutes. Not really sure what I'm going to do with this little guy just yet (why replace something that works?) but I have a distinct feeling it will fit in somewhere, somehow in the near future.

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