Wouter wrote:
>> If you just put a pullup
>> PNP on the RS-232 Tx line, with a 4.7K pulldown resistor to a half-wave
>> rectifier powered off the host PC Rx line, the RS-232 would be fine.
>
>Yeah, but that would add a few components.....
>

Unfortunately, the average time it takes *me* to double the number
of components in my h.w. designs (ie, T2x) is only about 5 minutes.
Similar regarding number of lines of code in my s.w. [guess it's in
the genes].

BTW, the RS-232 PNP pullup transistor circuit extends easily to
support the WouterBus.
===============

>> I haven't hashed out the exact code for a charge pump like you have
>> there, but it seems like one could use a 28-pin PIC, which has 2
>> hardware PWM outputs, set them as complements of each other going to
>> the intermediate diode tap points, and have a really nice stable
>> and adjustable Vpp generator.
>
>Vpp does not need to be adjustable (at least not for a 16x84), it must be
>(from memory) between 12 and 14V, and you can get away with somewhat lower
>once programming has been enabled by ~ > 12V. The Vpp generator just
>outputs a square wave, with the two pins at opposite polarities. The
>frequency must be high enough, and some extra pumping was needed after
>sending or receiving a char (which is 'busy wait', hence no pumping).
>

Yeah, for PIC programming, one Vpp level is ok. But for *general*
purposes, by extending this scheme using the 2 PWM outputs of a PIC28,
plus sensing the voltage using the PIC's A/D channel in a stabilization
loop, would make a really great "rock-solid" adjustable voltage
generator, good for about 0-13v. With the pump control timing produced
by h.w. PWM, rather than in s.w., there would be no droop when the cpu
performed other tasks, like RS-232. [Catching all this, Jim, re ebb?
I see an appnote coming].
==================

Wouter, think you could have your new '87x loader done by this weekend,
so Jim (Newton) could use it next week? [just kidding - keep up the
good work].

Thanks for all the comments and best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
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