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Finding the
Answer
Your answer is now found in this listing of the states +0000 through
+0004.
The 68000 always reads address locations 0, 2, 4, and 6 to find the stack
pointer location and memory location for the instruction it fetches after
power-up. The 68000 uses two words for each of the locations that it is
looking for, a high word and a low word. When the software designer
programs the ROM he must put the stack pointer location at address
locations 0 and 2. 0 is the high word location and 2 is the low word
location. Similarly, the high word of the instruction fetch location must be
in address location 4 and the low word in location 6.
Since the software design calls for the reset vector to:
1. Set the stack pointer to be set to 04FC,
2. Read memory address location 8048 for its first instruction fetch,
you are interested in what is on both the address bus and the data bus in
states 0 through 3.
You look at the following listing and see that states 0 and 1 do contain
address locations 0 and 2 under the ADDR label, indicating the
microprocessor did look to the correct locations for the stack pointer data.
You also see that the data contained in these ROM locations are 0000 and
04FC, which are correct.
Youthenlookatstates2and3. Youseethatthenexttwoaddress
locations are 4 and 6, which is correct, and the data found at these
locations is 0000 and 8048, which is also correct.
Using the State Analyzer HP 16510B
8 - 20 Front-Panel Reference