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The
Amélie
project | |
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Amélie consists of a number of hardware
components, the basic parts can be seen in the picture on
the right.
Part of Amélie's design philosophy is "keep it simple",
so only the minimum required is used. There is nothing
"fancy", as a system capable of rendering 3D images in
real-time may look good on paper, but it won't run your
heating any better, nor will it make a better burglar
alarm.
What
works is to keep it simple, keep it effective, and do
exactly
what is required with the minimum of fuss and
bother. |
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The
component parts of Amélie
are:
-
The
processor
A 6502, expected to be clocked at
2MHz; though I'll have to confirm that my VIA is
a 2MHz part as this will affect the overall
decision.
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The
"memory"
2K of static RAM, 8K of EPROM, and
memory-mapped I/O devices.
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The serial
I/O
A 6551 ACIA, running at 9600bps 8N1,
for communication with the "outside world". The
evidently-slow serial port speed is to allow communication
with pretty much anything, as well as not swamping
AmélieEm with serial port
interrupts. It will suffice, we aren't going to try
downloading megabytes of stuff, remember!
The 6551
requires a 1.8432MHz crystal to correctly
generate the baud rates, and it may be that this is used
as the master clock source (via the CPU, Ř2?). So long as
the VIA Timer1 period is adjusted to maintain a constant
50Hz 'ticker', then the actual system clock speed is not
really that relevant. In this case, 1843200÷50 is
36864, so this value should be loaded into Timer1 instead of the
40000 that 2MHz would
require.
Two components that do not have their own documents
are:
-
The latch. Mapped in at &A300 , this device appears as
a single byte in the memory map. The value written to this
byte is held until the next time it is updated (or 'latched',
hence the name). The lower four bits represent LEDs - bit 3 is red, bits 2 and 1 are yellow,
bit 0 is a green LED. The upper four bits
are unused.
-
 The options selector.
Optionally mapped in at &A200, this device is
basically a buffer wired up in 'reverse', which will make
the values of up to seven selection switches available to
the processor when addressed. This is not part of
the original Amélie specification, though I
mention it here as it may
be incorporated on the final
board. It only requires three components - a small IC
(a 74LS244), a resistor pack, and a bank of
microswitches.
The purpose of this is to provide a set
of "options" to alter various aspects of the behaviour of
the application code, without the need to "hardwire" the
desired options into EPROM and burn off multiple versions.
In the long run, the options selector is much more
efficient!
You will also find the memory map useful to look at, along with
the schematic (which may be found in the downloads
section). | |
© 2007 Rick Murray
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