Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!elee24
From: elee24@castle.ed.ac.uk (H Bruce)
Newsgroups: comp.sys.m6809
Subject: Choosing a microprocessor.
Message-ID: <5348@castle.ed.ac.uk>
Date: 26 Jul 90 11:49:17 GMT
Reply-To: elee24@castle.ed.ac.uk (H Bruce)
Organization: Edinburgh University Computing Service
Lines: 30

Since this appears to be the only group discussing low cost 8 bit micros here
I wish to ask some questions on the choice of uP for a project.

The project requires a low cost uP to control a 
frame grabber and a modem and to process
the images. A number of images will be captured, the first frame compressed
(using lossless DPCM) for transmission over a modem
and then the frame differences will be sent.
The images will be approximately 160 by 100 pixels.

Current thinking in the group is to choose an 8051 because it

* is widely supported (second sourced, high level language compilers)
* has a built in UART
* has scratch pad RAM
* has a hardware multiplier

However the 8051 is not ideally suited for accessing external RAM into which
the image will be mapped. For image processing functions the pixels in the image
may have to be accessed may times. Would a 6809 be any better at this - how long
does it a 6809 to read a byte from RAM ?
An 8051 running at 12Mhz would take 3us to move a pixel into the accumulator
for pixels with a 256 byte block.
(5us is both the lo and hi address pointers were loaded each time).
I am just worried about using a microcontroller for what I see as a
microprocesor application.

Thanks for your attention.

Henry Bruce