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Electronics query re 68000 CPU

J

jamma-plusser

Jan 1, 1970
0
What's the best way to pause a 68000 CPU? I'm diagnosing an old game
PCB and want to pause the screen so I can concentrate on fixing a hard
to track down graphics error.

Pausing it would help immensely.

No doubt I'll also have to disable any watchdog otherwise it will just
reset.

Thanks
 
J

JW

Jan 1, 1970
0
What's the best way to pause a 68000 CPU? I'm diagnosing an old game
PCB and want to pause the screen so I can concentrate on fixing a hard
to track down graphics error.

Pausing it would help immensely.

No doubt I'll also have to disable any watchdog otherwise it will just
reset.

Thanks

Drive the *HALT line to a logical 0.
 
J

JW

Jan 1, 1970
0
Thanks - could I just Ground it? Or should I use a resistor?

You could try a 1K resistor without hurting anything.
Do you have a schematic of the circuitry in question? What does the *HALT
pin connect to?
 
J

jamma-plusser

Jan 1, 1970
0
You could try a 1K resistor without hurting anything.
Do you have a schematic of the circuitry in question? What does the *HALT
pin connect to?

No schems I'm afraid.

Guess I could just try it - will do later.

Thanks
 
J

JW

Jan 1, 1970
0
No schems I'm afraid.

Guess I could just try it - will do later.

Usually shorting TTL outputs to GND won't hurt anything. Since the HALT
pin can also be an output from the 68K there's probably one or more open
collector devices driving this pin. As long as it's not tied to +5, I
doubt shorting to GND would hurt anything. To be even safer, you could try
a 100 ohm resistor if the 1K doesn't work, then try shorting to GND if the
pin is not tied to +5.

You're welcome.
 
J

jamma-plusser

Jan 1, 1970
0
Usually shorting TTL outputs to GND won't hurt anything. Since the HALT
pin can also be an output from the 68K there's probably one or more open
collector devices driving this pin. As long as it's not tied to +5, I
doubt shorting to GND would hurt anything. To be even safer, you could try
a 100 ohm resistor if the 1K doesn't work, then try shorting to GND if the
pin is not tied to +5.

Thanks, worked a treat. :)
 
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