HP 68302 User Manual page 113

Step 8. Set up the DTACK signals
Probably the least understood configuration options relate to the interlocking
and source for the DTACK signal. Selecting the options correctly is easy
once you know a little bit about your target system.
Selecting the DTACK sources for chip-selects CS0 through CS3 is easy. If
you will be programming a chip-select to generate DTACK internally (as is
most often the case) you should select "internal"; otherwise, select "external".
You may notice that the default for CS0 is "internal" and all others "external".
This is because the 68302 CS0 is configured to generate an internal DTACK
by default.
A somewhat more difficult option is "Emulation Memory Use Target DTACK".
Selecting this option will force the emulator to wait for your target system to
assert the DTACK signal whenever an access occurs to emulation memory
AND there is no internally generated DTACK for this cycle.
The "Emulation Memory Use Target DTACK" option is not selected by default
and can most often be left that way. When do you need to answer yes? If
ALL of the following are true:
Your target system asserts DTACK for some area of memory.
1
AND
2
Your target system inserts at least one wait state for that area.
3
AND
4
You are going to map that area as emulation RAM or emulation ROM.
5
What does this do? Interlocking DTACKs simply will ensure that the
emulation memory accesses to this area will have the same number of wait
states as your final target does.
What will happen if ALL of the above are true and you do not interlock
DTACKs? In the best case scenario, your code will run faster in the emulator
than it will in your actual target. This is because an area mapped as emulation
memory will always terminate with 0 wait states, even if it overlays an
address where your target system inserts wait states. Interlocking DTACKs
will ensure that the emulation memory accesses have the same number of
wait states as your target memory.
Chapter 4: Plugging the Emulator into Target Systems
Configuring the Emulator for In-Circuit Operation
113