Logic levels question 6502A (Missile command)
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high. This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game. Is this a normal value? I don't see any pull-ups on the address lines on the schematic. David _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
did you check that 3.3V line for ripple? check the cap filtering it? it has been a while since I did board repair so please excuse the email if it is way off base Art ----- Original Message ----- From: "David Shoemaker" <davids@oz.net> To: <rasterlist@vectorlist.org>; "'Technical Tools Mail List'" <techtoolslist@flippers.com> Sent: Saturday, November 05, 2011 2:33 PM Subject: [Techtoolslist] Logic levels question 6502A (Missile command)
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals... Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua etc. (Page 1-4, 6502 Instruction manual) John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
Well sounds like that theory is shot. I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there. I will check the voltage at the pullups. The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure. One thing about the rom test failing is the signature is not constant. Any other suggestions? Thanks, David -----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command) David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals... Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua etc. (Page 1-4, 6502 Instruction manual) John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
What really got me is I pulled all the roms, and put only the "bad" rom in. It passed the rom test on loop for 30 minutes no problem. I put the rom next to it back in and BANG right back to failures. But that second rom passes just fine. That is when I noticed the lowish address line values. -----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Rodger Boots Sent: Saturday, November 05, 2011 6:21 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command) If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/ _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
David Shoemaker wrote:
What really got me is I pulled all the roms, and put only the "bad" rom in. It passed the rom test on loop for 30 minutes no problem. I put the rom next to it back in and BANG right back to failures. But that second rom passes just fine.
That is when I noticed the lowish address line values.
Ah, with weird results usually I start looking at the IC sockets for problems. Perhaps a poor ground pin connection? continuity check may turn something up. Don't forget to unplug the pod when testing the buses/Vcc/Vgg with a meter otherwise your results can be invalid. John :-#)#
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Rodger Boots Sent: Saturday, November 05, 2011 6:21 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some
of
the ttl to not latch high.
This is checked through a meter using the fluke to read a particular
address
on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)#
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
Bus contention. Look at the chip selects simultaneously on those roms, they may be being selected at the same time if they work in-circuit fine on their own. The first rom is always selected, and is only deselected when another rom is looked at, this is normal operation. Andrew Welburn (mobile) www.andys-arcade.com On 6 Nov 2011, at 02:00, "David Shoemaker" <davids@oz.net> wrote:
What really got me is I pulled all the roms, and put only the "bad" rom in. It passed the rom test on loop for 30 minutes no problem. I put the rom next to it back in and BANG right back to failures. But that second rom passes just fine.
That is when I noticed the lowish address line values.
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Rodger Boots Sent: Saturday, November 05, 2011 6:21 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
There is something definitely going on odd with the data bus. I pulled all the roms and verified the pull-up resistors were good. I used the fluke to read address x7000 which should read FF as there is no rom there. I get a 00 read. If I hit repeat I get something else (like 3F), if I then hit loop it shows me some changing values then settles on FF. So there is something somewhere hitting the data bus at the same time. But using the probe on Address sync I am not finding any LS244's that are selecting at the same time. Going to go through them again on data sync. I may actually need to pull the logic analyzer out for this. Any suggestions on debugging this would be welcomed of course :) Thanks, David -----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Andrew Welburn Sent: Sunday, November 06, 2011 12:59 AM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command) Bus contention. Look at the chip selects simultaneously on those roms, they may be being selected at the same time if they work in-circuit fine on their own. The first rom is always selected, and is only deselected when another rom is looked at, this is normal operation. Andrew Welburn (mobile) www.andys-arcade.com On 6 Nov 2011, at 02:00, "David Shoemaker" <davids@oz.net> wrote:
What really got me is I pulled all the roms, and put only the "bad" rom in. It passed the rom test on loop for 30 minutes no problem. I put the rom next to it back in and BANG right back to failures. But that second rom passes just fine.
That is when I noticed the lowish address line values.
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Rodger Boots Sent: Saturday, November 05, 2011 6:21 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/ _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
I've had this on a Missile Command before. There's a LOT of various things that all hit on the data bus. If the wrong thing's getting enabled at the same time as you're trying to do a ROM read or check then you can see trackball data and allsorts in the results. Pain as it was to do, the way I got around it was to snip the enable line of every single buffer that was directly connected to the bus until the phantom data went away, at which point I'd found the source of the problem. Not desperately scientific, but it got the job done. Personally I find Missile Command's to be an absolute nuisance!! Martin. On 6 Nov 2011, at 23:22, David Shoemaker wrote:
There is something definitely going on odd with the data bus.
I pulled all the roms and verified the pull-up resistors were good.
I used the fluke to read address x7000 which should read FF as there is no rom there.
I get a 00 read. If I hit repeat I get something else (like 3F), if I then hit loop it shows me some changing values then settles on FF.
So there is something somewhere hitting the data bus at the same time. But using the probe on Address sync I am not finding any LS244's that are selecting at the same time. Going to go through them again on data sync.
I may actually need to pull the logic analyzer out for this.
Any suggestions on debugging this would be welcomed of course :)
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Andrew Welburn Sent: Sunday, November 06, 2011 12:59 AM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
Bus contention. Look at the chip selects simultaneously on those roms, they may be being selected at the same time if they work in-circuit fine on their own. The first rom is always selected, and is only deselected when another rom is looked at, this is normal operation.
Andrew Welburn (mobile) www.andys-arcade.com
On 6 Nov 2011, at 02:00, "David Shoemaker" <davids@oz.net> wrote:
What really got me is I pulled all the roms, and put only the "bad" rom in. It passed the rom test on loop for 30 minutes no problem. I put the rom next to it back in and BANG right back to failures. But that second rom passes just fine.
That is when I noticed the lowish address line values.
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of Rodger Boots Sent: Saturday, November 05, 2011 6:21 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
If you have it to one ROM it's probably the chip select line to that one part. And the signature changing would tend to indicate a timing problem such as a slow ROM or sloppy logic levels on that one line. On Nov 5, 2011 7:57 PM, "David Shoemaker" <davids@oz.net> wrote:
Well sounds like that theory is shot.
I pulled all the roms then using the fluke I did a read on one of the addresses looping. The fluke reports a series of values that builds up to FF (there are pullup resistors on all the data lines so I expected the value to be FF and stay there.
I will check the voltage at the pullups.
The fluke reports all ram tests ok (so I figure the 244's are ok). And only one rom reports bad. I checked it in my burner and it is fine there. I burnt a new one anyhow and it reported the same failure.
One thing about the rom test failing is the signature is not constant.
Any other suggestions?
Thanks, David
-----Original Message----- From: techtoolslist-bounces@flippers.com [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson Sent: Saturday, November 05, 2011 2:20 PM To: Technical Tools Mail List Subject: Re: [Techtoolslist] Logic levels question 6502A (Missile command)
David Shoemaker wrote:
I am trying to trouble shoot a board. I am getting some odd responses reading the roms. I noticed that the address lines coming from the 6502 seem to be going high at 3.5 - 3.7 vdc. I suspect this is causing some of the ttl to not latch high.
This is checked through a meter using the fluke to read a particular address on a loop and using my scope for the same and while running the game.
Is this a normal value? I don't see any pull-ups on the address lines on the schematic.
David
Don't forget the Fluke pod has it's own address and data line buffering. There are notes about watching out for that in the pod manuals...
Input Low Voltage ..... 0.8V max. Input High Voltage...... 2.0V min., +5.0V max. Output High Voltage ... 2.4Vmin. with loh = -250ua
etc. (Page 1-4, 6502 Instruction manual)
John :-#)# _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
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Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist FTP site is: ftp://ftp.flippers.com/TTL/TestEquipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/
participants (6)
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Andrew Welburn -
Art -
David Shoemaker -
John Robertson -
Martin White -
Rodger Boots