Can I get some suggestions from you clever lot please. I don't
use C, this will be in assembler

A PIC is connected to several analogue sensors. These sensors
have FSDs of 5V or 12V scaled down to 5V. A user inputs an
ASCII string so that the PIC will alert them when the sensor
meets the requirements of the string

For example, say the PIC was monitoring a 12V battery, the
ASCII sent might be L11, which means "alert me if the voltage
goes below (is "L"ess than) 11V". Similarly G (>) or E (=)

Right, here's the tricky bit

Taking the example above as a fairly simple implementation, I
know what the scale factor is (5:12) and that the highest result
from the A2D is 12V, so can work it out from there

What I really want to do is make a universal system so that any
ASCII string can be compared to any sensor voltage, so that the
user receives not only the alert but also a message in appropriate
terms and units

Another example, exaggerated but it shows what I'm after. A
temperature sensor has a 0-12V o/p, spanning the range 0C to
40C. The user sends the PIC "G20.58", meaning "alert me when
the temperature goes over 20.58 degrees"

Now there are two things to consider. First is the 5:12 scaling
of the input, second is converting the "20.58" to a variable that
can be compared to the A2D

I've tried a few things long-hand and wonder if there's a generic
way of doing it

First thing I tried was to search the string for a "." and then split
it. Working left from the "." I multiply by successive magnitudes
of 10, starting with a magnitude that depends on the position that
the number was sent to in an array. So "20" would be 0 x 1000
+ 2 * 10,000

But then realised I could maybe just pad either end with "0" and
convert the whole string to a number, then scale it in accordance
with the scale factor so that it could be compared. When sending
an ASCII message back, use inverse scaling. This would need to
be done (rather than simply echoing the original figure - eg "20.58
degrees reached) in case where the user is asking for an analogue
reading, in which instance the PIC would have to compose a
string from that reading in terms of the sensor's function and range

Strings (limited to 5 chars but all 5 not necessarily used) would be

y.xx
yy.xx
yyy.x

but if there's a simple way then covering .xxxx to yyyy would
be good (although they may be seldom, if ever, used)

I've spent a couple of days on this, and there still seems to be lot
of long-hand if...then, search this, search that coding ahead unless
I find a more elegant solution

TIA

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