On 9/26/06, Roy wrote: > To through a bit more light on my goal :-) > > I'm am thinking of making the circuit referred to in this application > note > > http://www.freescale.com/files/microcontrollers/doc/app_note/AN2342.pdf > > > The goal is to opto isolate the JTAG programmer section of my AVRdragon > programmer, will use to program ATMEGA ships with it. > > One aspect I was thinking of changing is to do away with the transistors > in the bidirectional section of the app note and use inverters as shown > in the unidirectional Fig 4. > > The reason for considering this is that the other JTAG lines will end up > with spare inverter gates. > > So I have played around with the Linear Technology spice program - see > attached jpeg. > One problem is the circuit you show is not isolated! :) I'm assuming this is to make spice happy. Two notes: 1) Check the opto speeds. You can buy fast ones now, but the normal ones are slow. 2) The circuit places a 330 ohm load on the target or the programmer each time the level changes. That is a pretty heavy load. Double-check the datasheets to see if its OK. If it's not, increase R4 and R5. Don't increase them too much, because they're effectively in series with the signal and could slow it down. Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist