Bruce Cannon wrote:
>Two pics is a fun idea, and I have worked through this same thought process
>as well with much the same conclusions as Morgan and Dan.  Ultimately I
>decided it was far easier and cheaper to use a more appropriate processor,
>but I'd also like to throw out the other thing I came up with:
>
>Epson's RTC-4574 will allow you to keep the PIC asleep almost all the time
>(having it wake on pin change).  This change can be an event outside the
>system, or one of the RTC's programmable intervals.  So you can use the
>internal oscillator, have your accurate time base, and very low power.  And
>the RTC periodic output could function as your watchdog as well, so you
>could skip using the PIC internal WDT for even lower power.
>
>Lastly, I don't think you can get the 15uA Dan mentions below when using the
>WDT.
>

Hi Bruce,

"... use a more appropriate processor ...." - ahh, a challenge,
say what.

Did you notice that most of the Epson RTCs cost $5-9 in small lots?

And I have been thinking more about the PICcybackPoacher [PCP]
idea. As rich+piclist [whoever he is] wrote, the PIC's oscillator
does not go off when you hold /MCLR low, so looks like you have to
use sleep mode.

Seems to me what would make a really nice system would be an
8-pin 12C67x running off a 32khz xtal. Have a 1-wire half-duplex
RS232 connection to the main PIC, used for both bi-directional
signalling and also INT [RB0] wakeup. You get the following:

- low-power 32khz RTC - 15uA.
- 1-wire RS232_comm/wakeup_interrupt channel.
- 3 PCP channels for "continuous" monitoring of critical external
  events - both analog & digital available [this is the "poacher"
  part - can be the same channels sampled by the main PIC].
- 128-byte additional RAM buffer in the PCP.
- continuous independent program execution in the PCP - programmable
  interrupt timing, alarm sensing, A/D limits, etc.
- using a 12CE67x gets you EEPROM store for saving config/etc.

You could also run the PCP off a 3v Li battery and talk to a
TTL-level PIC pin thru a series R and pullup - open-drain type
wired-and connection [with PIC running off 5v]. Unfortunately,
you cannot use RB0 interrupts with 3v on the PCP, since RB0 has
a schmitt trigger input Vih = 4v.

All in all, this gives you loads more functionality than a std
RTC chip for less price.

best regards,
- Dan Michaels
Oricom Technologies
http://www.users.uswest.net/~oricom
===================================


>Bruce Cannon
>Style Management Systems
>http://siliconcrucible.com
>(510) 787-6870
>1228 Ceres ST Crockett CA 94525
>
>Remember: electronics is changing your world...for good!
>
>
>> I really really like the PICcyBackWartPoacher idea, with a tiny PIC
>> like 12C6xx or an 18-pin'er, running at 32Khz, monitoring critical
>> I/O and A/D lines, and bringing up the big guy when needed. At 32khz,
>> you can get both continual [albeit slow] processing and very low
>> power draw, 15uA. Having a local net for comm/updates is good, or
>> storing/reading shared EPROM.
>>
>> best regards,
>> - dan michaels
>> ==============
>
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