Re: Horrid Serial Dacs

From: Andreas Hadler (Andreas.Hadler_at_t-online.de)
Date: 09/07/04 

Date: Tue, 07 Sep 2004 22:50:00 +0200

John Larkin <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote:

>Oh, I'm just coding up an embedded processor for an instrument that
>has three different kinds of serial DACs (Burr PCM56 and Maxim 5742s
>and 5205s) and they are all their own sort of mess. A few weeks ago I
>had to persuade some Analog Devices parts to work. One Max chip uses
>rising edge clock, the other is falling-edge. The 5742 has 35
>different serial commands.
>
>Bizarre.

I once had a project that cost me some days to figure out how to
connect some '165/'594, 2 DACs, an RTC, a serial EEProm and an ADC to
just one Motorola QSPI with automatic SPI scanning, using as less as
select pins as possible and allowing a fixed QSPI command and data
structure, only varying the QSPI start- and endpointer.
A real complex interaction of hard- and software, as different data
lengths, delays between commands and data answers, different edge
sensitivity, dead ends and feed-throughs etc. had to be considered.

It was not really kind of fun, more like an IQ-test with a lesson in
combinatoric. Nevertheless, it worked from the start.
Today, I consider it a lesson, what kind of design should be avoided
in low volume projects. It's just too complex to maintain in software
as well as in hardware. As they say in the software world:

Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it.
(Brian Kernighan)

and

Always code as if the guy that ends up maintaining and/or testing you
code is a violant psychopat who knows exactly where you live.
(unknown)

Have fun!

Andreas

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