Electronics query re 68000 CPU

J

jamma-plusser

Guest
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
 
On Fri, 29 Jan 2010 11:59:52 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b62cc82.668489296@news.zen.co.uk>:

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
Click to expand...
Drive the *HALT line to a logical 0.
 
On Fri, 29 Jan 2010 07:04:22 -0500, JW <none@dev.null> wrote:

On Fri, 29 Jan 2010 11:59:52 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b62cc82.668489296@news.zen.co.uk>:

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.
Click to expand...
Thanks - could I just Ground it? Or should I use a resistor?
 
On Fri, 29 Jan 2010 13:01:13 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b62dc07.672462265@news.zen.co.uk>:

On Fri, 29 Jan 2010 07:04:22 -0500, JW <none@dev.null> wrote:

On Fri, 29 Jan 2010 11:59:52 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b62cc82.668489296@news.zen.co.uk>:

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?
Click to expand...
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?
 
On Fri, 29 Jan 2010 09:30:13 -0500, JW <none@dev.null> 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?
Click to expand...
No schems I'm afraid.

Guess I could just try it - will do later.

Thanks
 
On Fri, 29 Jan 2010 14:44:28 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b62f424.678701890@news.zen.co.uk>:

On Fri, 29 Jan 2010 09:30:13 -0500, JW <none@dev.null> 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.
Click to expand...
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
Click to expand...
You're welcome.
 
On Fri, 29 Jan 2010 10:21:55 -0500, JW <none@dev.null> 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.
Click to expand...
Thanks, worked a treat. :)
 
On Fri, 29 Jan 2010 17:45:57 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b631ec0.689677015@news.zen.co.uk>:

On Fri, 29 Jan 2010 10:21:55 -0500, JW <none@dev.null> 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. :)
Click to expand...
You're welcome. Did you use a resistor, or just short to GND?
 
In article <5oadm5p9acp1495chorgkie9bdc09ci2vb@4ax.com>,
JW <none@dev.null> wrote:

On Fri, 29 Jan 2010 17:45:57 GMT jamma-plusser@hotmail.com (jamma-plusser)
wrote in Message id: <4b631ec0.689677015@news.zen.co.uk>:

On Fri, 29 Jan 2010 10:21:55 -0500, JW <none@dev.null> 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?
Click to expand...
Just for the record, a 68000 (along with just about every other
single-chip microprocessor ever made), is not TTL.

Isaac
 
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