On 6/29/2014 4:15 AM, Gerrit Heitsch wrote: > On 06/29/2014 06:53 AM, Jim Brain wrote: >> >> one pin will set RESET to 10V or 5V. Still working out how to create >> the voltage difference at the RESET pin. I can tie RESET to 5V through >> a IO pin and a diode, and then put a transistor on 10V PSU output, but >> then that will be 9.3V. I am not sure I have a 10.7V PSU output. > > How about something like they used on the tape port of the C64 or C16? > > A transistor with a 10.6V zener diode between base and GND plus a > pullup resistor between base and collector with the collector hooked > up to the PSU (which should supply about 14V). The emitter is > connected to the _RESET pin plus maybe a resistor to GND to allow for > some current flow. That takes care of the 10V. Now put another zener > (around 5V, might need some experimenting to find the correct value) > parallel to the first one, but only route it to GND via a gate from a > 7406 and maybe another gate from the same 7406 to pull the base of the > transistor to GND to allow for a reset. > > This way you need 2 portbits. One to switch between 10V and 5V and the > other allow for a LOW on the RESET pin no matter what the other one is > set to. > > Gerrit > > > > > Message was sent through the cbm-hackers mailing list Sorry, I should clarify: Still working out how to create.... using parts from my spare parts bin :-) 10.6 zeners are not in my bin right at present. It's OK, I took a 12V and dropped it through 3 PN junctions, so I think I'll have 9.9V... a diode and 10K feeds 5V to RESET, and two 2n3904s either dump 10V to the pin or drive it to ground. I'm cobbling together some code right now. Jim -- Jim Brain brain@jbrain.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2014-06-29 18:00:02
Archive generated by hypermail 2.2.0.