Ben,
use approx 4k7 pull down on the OSC1, ground the emitters of a NPN
transistor, use a 10k pull down from the base to ground and also connect
base to the pic via 470 ohm resistor

Wire the collector of this transistor to the base of a PNP transistor
through a 1k resistor with an additional 10k resistor from PNP base to
"12volt line", connect the PNP emitter to your "12volt" line.

Connect PNP collector to OSC1 and also a spare PIC pin with diode
pointing to OSC1. You will get approx .6 volts less out of the 12 volt
source due to emitter voltage drop, yo can fix this by inserting diode
between 7812 reg com pin and Gnd(pointing to Gnd)

Good luck !
regards, Graham Daniel
Ben Stragnell wrote:
>
> Hi all,
>
> I thought I'd try out the Scenix SX chips, (since they seem able to do
> everything a 16F84 can, but much faster :), but don't really want to
> spend $300 on the SX-Key programmer. So, I thought I'd have a shot at
> building my own. Since the SX chips I've ordered won't be here for a few
> days, I'm trying to get as much of the programmer built as I can in the
> meantime. I'm using a PIC 16F84 as an interface between the PC and SX.
>
> I've written the PIC code that will talk to the SX, and in order to test
> it, I've hacked together some PIC code that emulates a Scenix chip in
> ISP mode (128KHz timing signal, bidirectional data transfer, etc...)
> based on the Device Programming guide from www.scenix.com. So far, the
> two PICS talk to each other quite happily, so if the Scenix docs are to
> be believed, this part should work fine.
>
> Now, according to the Scenix docs, in order to get the SX into ISP mode,
> you have to drive OSC2 low, toggle OSC1 9 times (presumably at 5V),
> release OSC2, then raise OSC1 to 12.5V. This needs to be controlled by
> the PIC.
>
> I have a 12V supply, a 7805, and a 7812. It would appear that I need to
> be able to place the SX's OSC1 line at 0V, 5V and 12.5V, all under
> control of the PIC - and since I'm a programmer by trade, not an
> engineer, I have absolutely no idea how to proceed!
>
> If anyone has suggestions, I'd be grateful. Alternatively, if anyone's
> built a cheap scenix programmer, and released the schematics (couldn't
> find any on the web), that'd be cool too.
>
> Cheers,
>
> Ben

--
Steam engines may be out of fashion, but when you consider that an
internal combustion engine would require recovery of waste heat by
transfer just before top dead centre then fashion becomes rather
redundant, USE STRATIFIED HEAT EXCHANGERS ! and external combustion.

You heard it first from: Graham Daniel, managing director of Electronic
Product Enhancements.
Phone NZ 04 387 4347, Fax NZ 04 3874348, Cellular NZ 021 954 196.