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Chapter 4:Connecting the Emulator to a Target System
Plugging The Emulator Into A Target System
the target system clock signals EXTAL and XTAL and the processor. Others
implement entire clock crystal circuits.
The CLKO1 clock is the most important signal to the emulator because all system
timing is derived from this signal. For proper operation the CLKO1 clock signal
must always be available to the emulator. To provide this the default operation of
the 68360 is changed to enable the CLKO1 output at all times.
To enable the CLKO1 output, the emulator actually enters the background monitor
whenever leaving the hard reset state. This entry into the monitor is automatic and
occurs whether the emulator or the target system caused the hard reset. The
emulator only stays in the monitor long enough to set the CLKO1 output driver to
full strength. The CLKOCR is then write protected to prevent further writing to
this register. If the EMSIM (emulator copies of the SIM registers) register set is
valid these values will also be put into the CLKOCR at this time. Also if the
EMSIM set indicates that the upper address lines will be valid, then the monitor
will write to the PEPAR register so that these lines will be driven immediately.
When the background monitor is done making these modifications, the soft reset
line is pulsed to force the processor to restart its fetch of the reset vectors. What all
of this means to the target system is that following release of reset, there will be a
fetch from 0 which the emulator will trap as a bus error. Next the target system
will see no activity on the bus for several milliseconds while the monitor performs
its operations. Finally the target system will see a pulse of the RESETS signal
followed by the resumed fetching of the reset vectors.
Target power
The emulator uses power from the target system to operate the emulation processor
and some pullup resistors. Target power is sensed to make sure the emulator does
not drive the target system until the target is powered up.
Caution
Possible target system damage.
Because of the protections designed into the emulator, always power on the
emulator before powering on the target system. Always power off the emulator
after the target system.
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