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Chapter 4:Connecting the Emulator to a Target System
Selecting a clock module
If you have problems working with a target
oscillator
Typically an oscillator on the target system can be made to work with the emulator
by adjusting the signal quality with a termination. The Target Oscillator Clock
Module 64780-66509 connects the EXTAL line from the target system to the
processor. It also provides an RC termination on this signal. If no termination or a
different termination is required, a circuit can be constructed on a 14-pin header.
Use the schematic shown for the 64780-66509 as a guide.
If the EXTAL signal is not used on the target system, an internal oscillator can be
used as an alternative. The clock module socket is arranged so that a standard
14-pin DIP TTL oscillator can be used. Target system power is provided on pin
14, and ground on pin 7. The EXTAL connection to the processor is on pin 8. Pin
1 is pulled low so that oscillators with output-enable functions can be used.
If you have problems working with a target crystal
Using a crystal circuit on the target system with an emulator may be a problem,
especially when an accessory such as a flexible cable is used to connect the
emulator to the target system. Target Crystal Clock Module B of HP 64780-66507
simply connects the XTAL and EXTAL signals to the processor and provides a
typical value for the XFC bypass capacitance. If the PLL has problems
maintaining a lock, try selecting a different value for the XFC capacitance. Then
check to see if there is too much noise on the clock.
If the circuit will not oscillate or there is too much noise on the clock, use an
internal crystal circuit. If you are using either of the recommended standard crystal
frequencies, place the appropriate clock module in the clock module socket. Use
Module E of the HP 64780-66507 for 32.768 KHz operation, or use Module C for
4.194 MHz operation. Both these modules provide the correct crystal circuit for
use with the 68360, and a typical value for the XFC bypass capacitance.
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