HP 68302 User Manual page 116

Chapter 4: Plugging the Emulator into Target Systems
Configuring the Emulator for In-Circuit Operation
state -2
state -1
This trace shows how valuable the time stamp can be, not just in highlighting
cycles that are unusually long, but also in showing the effect of
reprogramming of OR1. You can see how the program fetch on line -11 took
approximately 600ns, but the program fetch on line -9 took only 280ns. This
is a result of the write to OR1 on line -10 which changed the internal DTACK
generation from 6 wait states to 1 state.
Many users capture a trace that shows the processor halting, but fail to take
the time to analyze the information in the trace. Examining a trace carefully
will often help you find the exact cause of a problem.
Step 10. Choose the correct target memory access size
Whenever the emulator accesses either target memory or an on-chip location,
it uses the monitor program to do so. The monitor program will use either a
"MOVE.B" or "MOVE.W" instruction for this access. You can control this by
selecting either "8 bits" or "16 bits" for the "Target Memory Access Size"
hardware configuration option.
The default value is "8 bits", and this should be acceptable for most cases.
There are cases, however, where a target system design allows only word
accesses to a particular area of memory, and you may wish to select "16 bits".
You may also find that you need the access size set to "8 bits" sometimes and
"16 bits" at other times.
116
The processor does a write of 0001 to location 43FFFEH as
a result of the instruction at -7, but because the the
chip-select that would provide DTACK has not yet been
initialized the cycle is not terminated normally. The
1.02mS time count is indicative of an internally generated
bus error (BERR).
Because of the bus error in the previous cycle the 68302
will immediately begin to process a bus error exception.
The first thing it will try to do is write the low word of the
program counter value to the stack. But again, because the
chip-select register has not been initialized, this stack write
will also fail with a bus error, hence the double-bus fault!