I'm confused about your reset circuit. It looks like the button will connect the Reset line to +5 but since the Reset is an active-low signal that makes no sense. Typically you would have Reset tied high with a pull-up resistor and use the button to connect it to ground to force a reset. Looks like that resistor might have been acting (through the LED) as a pull-up on your Reset pin? If you let the pin float the processor might be resetting.If the Z80 is a CMOS chip then all logic inputs must be pulled UP or DOWN. Floating inputs can cause two complimentary transistors to turn on at the same time and thus cause a short circuit between power and ground. That would cause the heating you noticed.
I'm wondering if the data pins are being used for output, perhaps during the refresh cycles. With the data lines tied to ground the processor will have to work hard if any of the pins are supposed to have a 1 output.
If you want the button to do a Reset you should provide a pull-up resistor on the Reset line and have the button ground the line.
Quote from: johnwasser on Jun 05, 2011, 06:15 pmIf you want the button to do a Reset you should provide a pull-up resistor on the Reset line and have the button ground the line.Yeah, this would be nice. So following your description, I put 2 x 10k resistors parallel between RST and the switch, and then connected the switch to the GND. Well, this doesn't work , so please tell me what connection should be used here?