From: hpoppe@ncar.ucar.edu (Herb Poppe)
Subject: Re: Command Control Standard Status Update
Organization: Scientific Computing Division/NCAR Boulder, CO
Date: Fri, 14 Aug 1992 21:27:27 GMT

In article <1992Aug12.183901.14259@pixar.com> Bruce@Pixar.com (Bruce 
Perens) writes:

> In article <4649@blue.cis.pitt.edu.UUCP> ebe+@pitt.edu (Elmer Beachley)  
> writes:
> 
> > with a open system, multiple sources and competition, will the demand
> > for this type of stuff every drive the prices low enough to meet the
> > goal of a $50 decoder?
> 
> Gosh, I don't see why not. Let's look at the hardware we are talking 
about
> here:
> 
> First, a simple embedded-controller microprocessor...
>...
> Now, if you can find me a microprocessor with built-in EAROM that fits
> in an 18-pin DIP or smaller, I can get this to fit in a Z-gauge tender.

It was suggested elsewhere that one of the Motorola 68HC05 might fit the 
bill. Unfortunately, the low pin count devices (the K1 and L2(?)) don't 
have the same timer system that the high pin count devices have. The 
latter timer system has very nice capabilities for measuring the timing of 
an input waveform (the CC on-track signal) and simultaneously generating a 
PWM output signal (motor speed). I found the timer system in the K1 and 
L2(?) disappointing. As I recall, none of the 68HC05 devices have on-board 
EEPROM (unlike many members of the 68HC11 family). Also, I don't think any 
68HC05 devices have Schmidt trigger inputs (which might be all that is 
necessary to clean up the on-track signal - after it is level-shifted).

I haven't yet found the "perfect" micro for this application (I've had 
this in mind for several years now), but it might be worth taking a look 
at the National Semi COP8722C (a member of the COP800C family). This is a 
20-pin, 8-bit device. It has 64 byte RAM, 64 byte data EEPROM and 1K byte 
program EEPROM. (Its sibling, the 8622, has 1K byte masked ROM.) It has 4 
Schmidt trigger inputs. It has a 1us instruction cycle time. The timer is 
a little weak (it can measure an input waveform or generate a PWM output 
waveform but not both at the same time). However, the timer could be used 
to generate a 50us (say) software counter which could be used to measure 
the input waveform (using edge-triggered interrupts from the on-track 
input signal) and generate the output PWM (every 50 us the software would 
check if it was time to toggle the PWM output - higher overhead that using 
the timer directly to interrupt the processor when the next output 
transition is desired). The 1K program EEPROM makes program development 
easier (for us low budget types) than other approaches. I don't know if 
the 8722 is available in a SMT package. Another feature of this chip is the
serial MICROWIRE PLUS interface which would allow it to interface to
additional micros - a digital sound system, for example.

Another useful IC would be a motor driver chip. I have used a 16-pin 
Sprague/Allegro device (forget the part number at the moment) for this 
purpose. It is an H-bridge with current-limiting and over-temperature 
shutdown. Not available in SMT to my knowledge. A smaller pin-count 
package would be desirable as well.

Herb Poppe                 National Center for Atmospheric Research (NCAR)
hpoppe@ncar.ucar.edu       1850 Table Mesa Dr.
(303) 497-1296             Boulder, CO  80303