Re: Wich 16-bit MCU?

"rickman" <spamgoeshere4@xxxxxxxxx> wrote in message
news:1151583021.913013.196990@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Robert Latest wrote:
Hello,

I'm now at the point where I'll have to dive into building an embedded
data acquisition system. Last time I did that was about 15 years ago --
burn-and-crash with an 68008 and an EPROM, much along the lines of
Chapter 11 in AoE (just to illustrate the point at which my uC knowledge
froze over).

What I need to do, in real-time, is this -- just to estimate the
workload the CPU has to cope with:

1. Read out one 16-bit ADC at 60 kHz rate, do a bit with the numbers and
write back out to an ADC at the same rate. This is a PI servo loop that
also could be done in analog hardware if the CPU isn't up to it.

<snip>

I think you are looking at needing a DSP rather than a CPU. Task 1 has
to "do a bit with the numbers" at 60kHz which is also known as having
16 uS to "do a bit" with each number you collect. You may be able to
get this done, but many CPUs will struggle at this rate depending on
what "do a bit" constitutes.

I'd agree with that. How clean is the input signal? If you need filtering
too (and I'd bet you do), that takes cycles.

I recently did a PID loop with an H8 (3048F variant). Input signal was
noisy, filtering was necessary. My CPU maxed out at under 1k loops/second,
which was more than good enough for me, but a couple of orders of magnitude
too little for you.

Or indeed consider the analogue PI alternative. But as Rickman says, 60kHz
is a fair old whack.

Steve
http://www.fivetrees.com


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