🚀 go-pugleaf

In article <29569@castle.ed.ac.uk> wbg@festival.ed.ac.uk (W Geake) writes:
>In order to run an analogue to digital convertor module from a serial
>port, I want to send a byte from the port every 10 ms.  This sets the
>sampling rate, so the accuracy of the interval is very important.  The
>VB Programmer's Guide mentions BUILT IN POTENTIAL FOR ERROR in timer
>controls, a great euphemism if ever I heard one.  Can I get good precision
>from VB, or do I need to work in C (please not!) or C++(worse still) or
>write a VxD (I'd rather sell life insurance)?

Bill, you have a fairly hairy problem on your hands.  In order to get that
rate, you are going to have to grab one of the timers (probably the keyboard
scan timer) and reprogram it to 100 Hz.  Then you are going to have to install
a custom interrupt handler to pump the serial port.  And you STILL have to
worry about DOS or something else taking over your machine for many milliseconds
while it does something it thinks is more important.

If I were in your shoes, I would grab a microcontroller or a single-chip
microcomputer and dedicate it to pumping the ADC.  If all you need is a pulse,
just so the ADC module gets SOMETHING, then something like a Motorola 68HC705K1
would probably work just fine.  If you need a real-live character, then an 8751
or something along those lines (68HC11, say) would work well.  (Note: I am
extremely fond of the New Micros Inc. F68HC11: it comes with Forth blown into
the on-board ROM.)

In article <29569@castle.ed.ac.uk> wbg@festival.ed.ac.uk (W Geake) writes:
> In order to run an analogue to digital convertor module from a serial
> port, I want to send a byte from the port every 10 ms.  This sets the
> sampling rate, so the accuracy of the interval is very important.

If you want to do something every 10 ms, on an IBM clone, you have to:

	1. Write a device driver to do the work on a timer interrupt.
	2. Deal with the standard timer interrupt, which runs at 18.2 Hz.
	   a. Make it run faster and then emulate the standard speed
	      for the rest of the system
	   b. Install a secondary clock for the device driver.
	   c. Use a video card that lets you work off the vertical
	      blank interrupt and runs at 100 frames per second.

Needless to say, you can't do this in Visual Basic, and doing it in
C or C++ is going to require a lot of effort coercing the compiler
to do the interrupt routine. I think you've got some assembler ahead
of you.

> (I'd rather sell life insurance)?

I used to sell encyclopedias door to door, when I was at school. Is
that anything like it?
-- 
Peter da Silva                                            `-_-'
Ferranti International Controls Corporation                'U` 
Sugar Land, TX  77487-5012 USA
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