Homemade computer
I've constructed a little 8 bit system myself. At the time of developing the
board described below, I was quite interested in these old
8 bit machines, especially in the very easy to program
6502 CPU. The main thought is to get
a very simple computer capable of controlling
external hardware like chipcard readers or similar things. A Linux PC can
connect via a standard interface (e.g. serial interface) to this little system.
If the system crashes due to a programming or hardware error it is back up
again after a few seconds as the whole OS is stored in ROM. Today one could
construct a board holding a 32 bit system with sufficient power
to run a Linux system.
Update (Aug. 2005): I'm engaged constructing and programming a
32 bit computer system based on the ARM architecture. This system is
running Linux now. You can take a look at it.
RDS decoder
In 1994 I designed a small RDS decoder board as an interesting application.
I built the system and designed an operating system to process the RDS data,
control the keyboard and the LC display. The LC display is one of those
ready to run 2*16 character displays but the connection to the CPU bus
is an idea of myself needing only a 74LS245 buffer. In short words: It is an
interesting challange to built such a computer.
Description
On the right side you can see the running RDS decoder mounted on
the printed circuit connected
to the RDS signal preprocessing, the display and the keyboard.
At the moment of taking the photo the radio was tuned to the
german radio station Bayern3.
As you can see the computer is built with a 65C02 CPU, an
8 KByte EPROM, a 2 KByte RAM and a 65C22 I/O (VIA) port that
receives the digitized RDS data, controls the LEDs and the
keyboard. The CAT-5 cable delivers the RDS data in digital
format from the receiver (Already digitized, not shown in image).
A nice feature of the software is the automatic calculation of
data and time from the "CT" signal of the RDS data. The time is
shown on the right side of the first row, the tuned station on
the left side of the display. So the first 16 characters are
always used.
The second row shows the information the users wishes to see.
In the image you can spot a little extract from the radiotext
of Bayern3. As the software is completly written by myself,
it is even possible to see "gimmicks" like the
program-identificationcode.
You can select between radiotext, date and time, alternative frequencies,
program-identification code, program type, traffic announcements,
musik or speech transmission flag and various flags.
Schematics and operating system
For the interested, the software for
the RDS decoder is avilable for download. The software is covered by the
GPL, the one who want to use the code as a base for own ideas is welcome
to do so. Together with the board schematic sheet you can even built your
own decoder board.
A better view on the details is also
available.
You can assemble the code into the binary with the assembler
dasm on your Linux system. Informations and download
of dasm on
www.ibiblio.org.
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![[ Image: Small view of the decoderboard. I recommend downloading and viewing it ]](pictures/RDS-Dekoder-in-Action.jpg)
