Step 1. Understand The Important Concepts - HP 64746 User Manual

Chapter 5: Plugging into a Target System
Configuring the Emulator for In-Circuit Operation

Step 1. Understand the important concepts

There are a few basic concepts related to 68302 emulation that should be
understood before you begin. Understanding these concepts will help you avoid
the common startup problems.
Accessing Memory that is Enabled via a Chip Select
Nearly all 68302 target systems rely on the built-in chip-selects for at least some
accesses to memory. The important concept to remember is that the 68302
emulator does not automatically setup any chip-selects for you other than
chip-select zero, which is automatically setup by the 68302 itself.
If you attempt to access memory that is dependent on a chip-select being
programmed, without first ensuring that that chip-select is programmed, some type
of failure will result. This most often causes problems when you are trying to do
commands such as load memory, display memory, run, or step.
Setting the Interrupt Mode to Dedicated or Normal
The 68302 has two basic types of external interrupts, referred to as Normal or
Dedicated mode. In Normal mode, three lines are used to indicate interrupt levels 0
through 7 or no interrupt. This normal mode scheme is just like the one used on
traditional 680X0 devices. In dedicated mode, the three lines each have a dedicated
purpose, one for each of the interrupts level 1, 6 and 7.
Why is this important? The emulator uses a level 7 interrupt to accomplish what is
known as a "break" from the user program to the emulation monitor program. The
monitor is needed for tasks such as display/modify of target memory and 68302
registers, as well as single-stepping. In order to initiate a level 7 interrupt, the
emulator must know what interrupt mode the 68302 has been programmed for. An
emulator configuration question is used to indicate which mode the 68302 will be
in. If the 68302 is not in that mode when a break is attempted, the break will either
fail, or lead to unexpected interrupts.
Note that although the 68302 emulator uses the level 7 interrupt, you are free to use
the level 7 interrupt for your own purposes. This is because the emulator is able to
differentiate between a target system-generated interrupt and and an
emulator-generated interrupt.
150