| ??? 09/20/04 20:57 Read: times |
#77749 - RE: AT89S8252 ISP via SPI Responding to: ???'s previous message |
Is this schematic the ISP part of your circuit or just a standalone programmer? It's just the ISP part of my circuit which is, for now, the entire circuit. 1) I don't see any decoupling capacitors. They're there. I have 0.1uF between the Vcc of each IC and ground. 2) Don't leave the unused input of the latch as unconnected. I went ahead and grounded the unused 4 inputs. No change in results. 3) For the time being, remove the pull down resistor (at RST signal from parallel port) and generate RESET from PC. Or relocate the reset capacitor to the resistor side if you need a POR as well. You will need 10uF capacitor with 10K resistor. Actually I just looked at the schematic again and I see that that's an earlier version. The 10uF capacitor and 10K resistor are already on the MCU side of the latch. In any case, the reset signal doesn't seem to be the problem. That seems to be getting to the MCU fine. The problem seems to be the MISO line going back to the PC. Regards, Craig Steiner |
