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From: Hugh Blemings <hugh@Sw2.canberra.edu.au>
Subject: Re: MCU advice? 
In-Reply-To: <CRYAN.94Dec29122805@class.iona.ie> 
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Date: Fri, 30 Dec 1994 09:05:23 +1100
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On 29 Dec 1994, Craig Ryan wrote:

Hi Craig,

In your post regarding using 'HC11's for an automotive application...

> 	- is this the best MCU to use and if so, which variation is best
> 		E9, E20 etc (programming/use/performance wise)

I think the HC11 would be ideal, depending on the amount of processing
required, if you're trying to do anything really heavy you may want
to look at a DSP or DSP/MCU combination.

It's a while since I've lloked at the data but the E9 part would be a 
good choice, I think it will run at up to 3MHz, has a heap of EPROM, some
EEPROM and some RAM.  The latter two memory types could be your
prime concern depending on how much data you want to store locally.
If necessary, it is easy enough to add external memory at the cost of 
losing some I/O.  Obviously you'll want to look at the ceramic windowed
version for development work ;)

> 	- what is the cheapest way of programming them?

Motorola made a programmer board which were about AUS$150 ($US100 ish)
several years ago, hosted off a MAC/PC serial port it allowes the
on board EPROM to be programmed via the MCU's bootstrap code.  It would 
be fairly trivial to build in a bootstrap programming mode to your board
if you prefer.
 

> 	- the E series have various modes for EPROM programming but is it
> 		cheap/easy to erase? How? Is it easier to go for a
> 		seperate EEPROM? If so, is it a simple matter to connect
> 		it to the MCU? Can I program a seperate EEPROM using E 
> 		series programming modes?

The EEPROM is pretty easy to program, I suggest you avail yourself of a
HC11 data book if you've not done so already, the issue I have has
a pinkish (no, really!) cover.  You can connect an external EEPROM if you
like but in either case you must provide your own programming code or
use the example in the data book.  Erasing the EPROM memory is done
with a regular UV light source.  Bear in mind the EEPROM memory has a
limited (10,000 to 100,000) write cycle life so RAM is probably better
for data storage.  I've always tended to use the EEPROM for code or
parameter storage.

> 	- would it be simple to connect the pulse from something like
> 		a car coil to one of these? 

Yup, you'll need some pretty careful filtering etc. to remove the unwanted
gunk.  Opto isolation is worth considering also.  By using one of the
devices' ICn (Input Capture) pins you can generate an interrupt and capture
a timer value when a pin transitions.  I used this earlier on in my
work with the HC11 for a car tacho with some success.

> 	- are there any relevent books about MCU projects etc which are
> 		worth looking at?

I imagine so, I regret I'm too out of touch to suggest any!!

Just my $0.02 :)

Regards,
Hugh

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 Hugh Blemings                         |
  email : hugh@Sw2.canberra.edu.au     |  phone : 015 485558 / +61 15 485558
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