Pocket Serial Host Acts As An Apple II Disk Drive

February 6, 2013 by Mike Szczys 21 Comments

apple-II-pocket-serial-host

[Osgeld] is showing off what he calls a sanity check. It’s the first non-breadboard version of his Pocket Serial Host. He’s been working on the project as a way to simplify getting programs onto the Apple II he has on his “retro bench”. When plugged in, the computer sees it as a disk drive.

The storage is provided by an SD card which is hidden on the underside of that protoboard. This makes it dead simple to hack away at your programs using a modern computer, then transfer them over to the retro hardware. The components used (starting at the far side of the board) are a DB9 serial connector next to a level converter to make it talk to the ATmega328 chip being pointed at with a tool. The chip below that is a level converter to get the microcontroller talking to the RTC chip seen to the right. The battery keeps that clock running when there’s no power from the 5V and 3.3V regulators mounted in the upper right.

The video after the break shows off this prototype, the breadboard circuit, and a demonstration with the Apple II.

Continue reading “Pocket Serial Host Acts As An Apple II Disk Drive” →

Learn A Little Assembly Language For The 6502 Processor

February 5, 2013 by Mike Szczys 29 Comments

6502-assembly-tutorial

Evern wanted to write your own Atari 2600 games? This won’t get you quite that far, but it will teach you the very basics. It’s an assembly tutorial for the 6502 processor. The nice thing is that you need nothing more than your browser to participate thanks to the embedded JavaScript emulator which acts as assembler, machine, and debugger in one.

The 6502 was in a lot of early equipment. In addition to the previously mentioned Atari they can be found in the Commodore 64, Apple II, and the original NES. You can even find folks building their own computers around the chip these days (most notable to us is the Veronica project). The guide starts off slowly, providing a working program and challenging the reader to play with to code in order to alter the outcomes. It moves on to an overview of registers and instructions, operators and branching, and culminates in the creation of a simple game.

[Thanks Mathilda]

How The 8085 ALU Is Structured

January 25, 2013 by Mike Szczys 10 Comments

8085-alu-reverse-engineering

This is a microscopic photograph of an 8085 processor die. [Ken Shirriff] uses the image in his explanation of how the ALU works. It is only capable of five basic operations: ADD, OR, XOR, AND, and SHIFT-RIGHT. [Ken] mentions that the lack of SHIFT-LEFT is made up for by adding the number to itself which has the effect of multiplying a number by two; the same mathematical function performed by a shift operation.

His post details the gate arrangement for each ALU operation. This is clear and easy to follow, and was based on reverse engineering work already done by a team who meticulously decapped and photographed the dies.

Not long ago this explanation would have been voodoo to us. But we worked our way through The Elements of Computing Systems text-book by following the online Nand to Tetris course. It really demystifies the inner working of a chip like the 8085.

Now if you really want to understand this ALU you’ll build it for yourself inside of Minecraft.

[Thanks Ed]

Google Talk Bot Running On Raspberry Pi

January 17, 2013 by Mike Szczys 13 Comments

google-talk-raspberry-pi

[Michael Mitchell] put together a demonstration of how Google Talk can be used to communicate with scripts. Although the concept isn’t new we haven’t seen very many projects that use the chat interface for issuing commands and receiving data. The one that does come to mind is this home automation project which uses Google Talk because it’s quite a bit faster than SMS or email communications.

Luckily there’s already a Python library called pygtalkrobot which helps with the XMPPPY protocol used by Google Talk. In addition to that package, [Michael] also installs some extras which allow him to access the GPIO pins on the RPi via Python. In the video after the break he demonstrates switching and LED on and off, as well as reading from a slide switch connected to pin 8. Of course it’s a snap to code feedback from the OS itself. As you can see in the image above the RPi is reporting it’s uptime after being issued a command by [Michael]

Continue reading “Google Talk Bot Running On Raspberry Pi” →

Veronica VGA Board Finalized

January 11, 2013 by Mike Szczys 16 Comments

veronica-vga-board-finalized

The latest update in the Veronica 6502 computer project is this finalized VGA board which now has a home in the machine’s backplane.

We’ve been glued to the updates [Quinn Dunki] has been posting about the project for many months now. Getting the GPU working proved to take quite a bit of time, but we learned a ton just by following along. The video output had humble beginnings way back in March. That breadboarded circuit got complicated very quickly and that was before it was even interfaced with the CPU. As you can see from the image above, etching and populating the GPU board really cleans up the build. We’re sure it’s robust enough to move around at this point. We wonder if she’s planning on showing it off at a Maker Faire or another geeky gathering?

It really has become clear how wise [Quinn] was to design a backplane board early on. It plays right into the modular concept. She was even smart enough to include that SIL pin header on the near side of the board which was used heavily while prototyping this video module.

Bluetooth Network Monitor

January 11, 2013 by Eric Evenchick 20 Comments

[Zak] wanted to keep tabs on his network connection without needing to log into his router. Since his router was a PC running Debian Linux, he rigged up a Bluetooth Network Monitor to display the information.

The monitor is based on a ATMega328P that reads data from a Bluetooth serial connection and displays it on the TFT screen. It uses a low cost Bluetooth module to receive data from a router. A shell script fetches the data and formats it into a string that can be sent over the Bluetooth link.

A USB connection with a desktop computer is used to power the device, but [Zak] also added USB support using V-USB. He plans to use it to get data from the desktop. For example, he could display CPU load and temperature data.

Overall, this is a nice project for fetching data wirelessly and displaying it on your desk. [Zak] has provided the code and Eagle files with his write up for anyone interested in building their own.

Interfacing A GPU With A CPU

December 26, 2012 by Mike Szczys 11 Comments

interfacing-a-gpu-with-a-cpu

[Quinn Dunki] pulled together many months worth of work by interfacing her GPU with the CPU. This is one of the major points in her Veronica project which aims to build a computer from the ground up.

We’ve seen quite a number of posts from her regarding the AVR-powered GPU. So far the development of that component has been happening separately from the 6502 centered CPU. But putting them together is anything but trivial. The timing issues that were so important to consider when developing the GPU get even hairier when it comes writing to the VRAM from an external component. Her first thought was to share a portion of the external RAM between the CPU and GPU as a way to push rendering commands from one to the other. This proved troublesome both in timing and in the number of pins available on the AVR chip. She ended up using something of a virtual register on the AVR chip that can receive commands from the CPU asynchronously. Timing dictates that these commands be written only during vertical blanking so this virtual register also acts as a status register to let the CPU know when it can send the next command.

Her post is packed with the theory behind the design, timing tests on the oscilloscope, and a rather intimidating schematic. But the most important part is the video showing her success in the end.