Quote:
Originally Posted by ischmitz
Hardtailer,
unfortunately your oscilloscope seems to have very limited bandwidth and is sampling to where the signals are aliasing and thus not making a lot of sense. But here are the simple things that need to happen in the following order:
- The MCU needs power (+5V and GND)
- Pin 18 and 19 need the 6MHz clock from the quartz
- Pin 7 RST needs to transition from low to high to bring the MCU out of reset.
With that you need to see the ALE output on pin 30 generating a 1Mhz square wave. If that isn't happening MCU is dead and you need a replacement.
Then the MCU starts reading and processing code from the EPROM and that will generates the 80 Hz square wave ICV signal on pin 5. And that ICV signal serves the watchdog keeping it from resetting the MCU. If the watchdog doesn't see the ICV signal coming from pin 5 it will pull the reset line low for a short time and then release it back to 5V. If that process repeats you are seeing a square wave on pin 7.
The ICV signal can be missing because:
a) MCU is not powered or damaged
b) EPROM is not present or inserted incorrectly
c) Wrong EPROM or corrupted data burned to EPROM
d) The 74LS373 is damaged
e) Another component on the address or data bus causes issues
All this needs to work before you put any flywheel signals into the box
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Wrong MCU, my 8051 datasheet indicates pin 9 & the run mode is a low;
