Andreas Freiherr wrote:
> My "self-made 6809 computer" project addresses the problem of complexity
> vs. functionality by composing the machine from modules. This way, you
> can add another low complexity module whenever you want additional
> functionality.
>
> The core is a board housing the processor, 60k of RAM and 4k of ROM,
> with 256 bytes masked out of the address space in a decoder. I developed
> this idea and later heard of the I/O space used in PDP-11 architecture.
> It is 4k in the PDP-11, but it is the same idea. Why shouldn't it work
> for me, too? The address space is layed out in a way that should make it
> easy to eventually replace this board with separate boards with CPU and
> MMU on one of them, plus one or more memory modules.
Better check to see how OS/9 level II is memory mapped. I think the
last 256 bytes
are common to all memory maps. Lets not forget the PDP-11 went from a 18
bit bus to I think a 22 bit bus.
> A separate module has two 6850 ACIAs to provide two serial interfaces,
> complete with 1488/1489 drivers/receivers and COM8116 (or something like
> that) programmable baud rate generators, the board even supports
> split-speed operation for applications like BTX (50 baud send, 1200 baud
> receive).
Nice. I like the maxim chip out that uses +5 volts and generates local
+-10 volts for RS232 buffers. This chip and 2 memory chips are wired to
FPGA prototype board to give me a minimal computer system. I am slowly
working on the PCB board with a limited front panel and a choice of
bootstraps: Front panel, serial port , EEPROM. The primary bootstrap at
the moment is the serial port as I download test programs from a PC to
test my CPU design. In time I will have a floppy disk and my system will
be stand alone.
> To provide an easy way of configuring the hardware, I created a board
> with 8*8 DIP switches. The idea is to put these switches as 8 readable
> bytes at a fixed address and use them to provide initialization
> parameters to the ROM based monitor program. This board also came in
> handy in initial testing of the processor board: I managed to squeeze a
> 9 byte loop into these 64 switches that made a LED on the processor
> board (address decoder output) blink when running properly.
Neat.
> A video board (with capabilities slightly above a VT100) exists on paper
> only, an EPROMmer on another board was partly built when time ran out.
> All that stuff is still around, and I have a 19" rack mount frame that
> contains the self-made power supply (with 24V ready to support 8" floppy
> drives) and up to ten of my wrapped boards.
I would like to see that.
> All this is based on standard components, but intentionally incompatible
> to existing buses: I wanted to force myself to build everything on my
> own. Once I dig down to those pieces, I may be able to provide some
> pictures. Stay tuned ;-)
Ok ... but the picture is a bit wavy :)
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html
Received on Sun Mar 31 2002 - 17:35:14 BST