Electronics query re 68000 CPU
 

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

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 11:59:52 GMT (jamma-plusser)
wrote in Message id: :

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.

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 07:04:22 -0500, JW wrote:

On Fri, 29 Jan 2010 11:59:52 GMT (jamma-plusser)
wrote in Message id: :

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.

Thanks - could I just Ground it? Or should I use a resistor?

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 13:01:13 GMT (jamma-plusser)
wrote in Message id: :

On Fri, 29 Jan 2010 07:04:22 -0500, JW wrote:

On Fri, 29 Jan 2010 11:59:52 GMT (jamma-plusser)
wrote in Message id: :

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.

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?

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 09:30:13 -0500, JW wrote:


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?

No schems I'm afraid.

Guess I could just try it - will do later.

Thanks

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 14:44:28 GMT (jamma-plusser)
wrote in Message id: :

On Fri, 29 Jan 2010 09:30:13 -0500, JW wrote:


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?

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.

Thanks

You're welcome.

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 10:21:55 -0500, JW wrote:


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. :-)

Electronics query re 68000 CPU
 

On Fri, 29 Jan 2010 17:45:57 GMT (jamma-plusser)
wrote in Message id: :

On Fri, 29 Jan 2010 10:21:55 -0500, JW wrote:


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. :-)

You're welcome. Did you use a resistor, or just short to GND?

Electronics query re 68000 CPU
 

In article ,
JW wrote:

On Fri, 29 Jan 2010 17:45:57 GMT (jamma-plusser)
wrote in Message id: :

On Fri, 29 Jan 2010 10:21:55 -0500, JW wrote:


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. :-)

You're welcome. Did you use a resistor, or just short to GND?

Just for the record, a 68000 (along with just about every other
single-chip microprocessor ever made), is not TTL.

Isaac