HP 64746 User Manual page 151

Chapter 5: Plugging into a Target System
Configuring the Emulator for In-Circuit Operation
The Freeze Pin and the Background Monitor
The 68302 has a hardware input pin called FRZ which can be used to "freeze"
selected on-chip peripherals. When configured for the background monitor, the
68302 emulator will assert the FRZ pin during the entire time the emulator is
running in the monitor.
If you are using the SCC functions of the 68302 or the built-in DRAM refresh
feature you will most likely want to configure your emulator for use with the
foreground monitor since these functions will be "frozen" during all background
monitor operation. "Step 5. Decide whether to use the foreground monitor" will
further explain these issues.
While running in the background monitor the watchdog timer will not be serviced.
However, knowing that the FRZ pin is asserted during background monitor
operation makes it easy for you to freeze the watchdog timer during this time.
Freezing the watchdog timer will be discussed later.
On-Chip Locations
Most of the special features of the 68302 are controlled via a 4 Kbyte block of
on-chip locations (RAM and special registers). The address of that 4 Kbyte block
is determined by the value written to the BAR. When you configure the emulator
you must map that 4 Kbyte block of memory as target RAM. Mapping that block
as "guarded" or "emulation" memory will prevent proper operation or result in
guarded memory access errors.
Any display or modify of on-chip locations, including registers, requires the
emulation monitor program. If you do a display or modify of these locations or
registers while running your program, the emulator will briefly break into the
monitor, perform the display or modify, then return to your program.
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