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What Am I
Going to
Measure?
You decide to start where the microprocessor starts when power is
applied. We will describe a 68000 microprocessor; however, every
processor has similar start-up routines.
When you power up a 68000 microprocessor it is held in reset for a
specific length of time before it starts doing anything to stabilize the
power supplies. The time the microprocessor is held in reset ensures stable
levels (states) on all the devices and buses in your circuit. When this reset
period has ended, the 68000 performs a specific routine called "fetching
the reset vector."
The first thing you check is the time the microprocessor is held in reset.
You find the time is correct. The next thing to check is whether
the microprocessor fetches the reset vector properly.
The steps of the 68000 reset vector fetch are:
1. Set the stack pointer to a location you specify which is in ROM at
address locations 0 and 2.
2. Find the first address location in memory where the microprocessor
fetches its first instruction. This is also specified by you and stored
in ROM at address locations 4 and 6.
Whatyoudecidetofindoutis:
1. What ROM address does the microprocessor look at for the location
of the stack pointer, and what is the stack pointer location stored in
ROM?
2. What ROM address does the microprocessor look at for the address
where its first instruction is stored in ROM, and is the instruction
correct?
3. Does the microprocessor then go to the address where its first
instruction is stored?
4. Is the executable instruction stored in the first instruction location
correct?
Using the State Analyzer HP 16510B
8 - 2 Front-Panel Reference