Without the ROM installed the processor is running nonsense code so there is not much to be gleaned from what happens.
When you are capturing data with your LA are you doing a hard reset, i.e. hold down CTRL+BREAK+press reset. This causes the machine to try to initialize everything and copy the code from ROM to RAM that I mentioned before. Jeff Brt From: M100 <m100-boun...@lists.bitchin100.com> On Behalf Of Eric Sent: Tuesday, January 2, 2024 7:31 PM To: m100@lists.bitchin100.com; m...@bitchin100.com Subject: Re: [M100] Model 100 - LCD Shows Pixels Only I had an interesting finding: With the M12 ROM installed, pin 20 (A11) is stuck in a high state (5V). With the M12 ROM removed, all address lines are in a high state except for pins 3 (A7) and 7 (A3). Measurements taken at the ROM socket. Eric On Monday, January 1, 2024 at 08:53:52 PM PST, Brian K. White <b.kenyo...@gmail.com <mailto:b.kenyo...@gmail.com> > wrote: Anything anywhere on the bus could be holding an address line high since they're all attached to essentially the same wire, so, pull the main rom, see if it's still stuck. If so, pull the ram even though that does mean desoldering which requires some care & technique to avoid damaging the motherboard. The execute basic might be normal because there is a feature in the main rom to run a certain program at boot if it's been set up, kind of like autoexec.bat. I don't remember the specifics but it's in the regular user manual. But you're right that right now that doesn't matter because all bets are off and no data matters no matter what it looks like until that address line is unstuck. -- bkw On 1/1/24 18:27, Eric wrote: > Happy New Year Everyone! > > After probing around, I found that M12 ROM Pin # 20 (A11) is stuck high > (5V). Does this suggest a faulty ROM or is there something else that > could cause this condition? The ROM chip is a SHARP LH535618. Computer > serial number starts with 307xxxxxx. > > I also have data from the logic analyzer (big thanks to Jeff Birt and > his videos). Data was taken during a Cold Boot. It seems that the > computer is skipping the "Boot Routine" and attempting to run and > endless loop of 0804H "Execute BASIC program". There also appears to be > a lot of garbage data. This may not be entirely meaningful being that > ROM pin A11 is stuck high. > > Eric > > > On Friday, December 29, 2023 at 06:18:35 AM PST, bir...@soigeneris.com > <mailto:bir...@soigeneris.com> > <bir...@soigeneris.com <mailto:bir...@soigeneris.com> > wrote: > > > Eric, > > Sent you a mail off list with a link to my capture files, etc. > > Jeff > > *From:* M100 <m100-boun...@lists.bitchin100.com > <mailto:m100-boun...@lists.bitchin100.com> > *On Behalf Of *Eric > *Sent:* Friday, December 29, 2023 2:00 AM > *To:* m...@bitchin100.com <mailto:m...@bitchin100.com> > *Subject:* Re: [M100] Model 100 - LCD Shows Pixels Only > > Hi Jeff, > > Luckily my logic analyzer does have more than 8 channels. > > Can you give me some feedback on these settings: > > Chip M2 TC40H245P - Octal Bi-Directional Bus Buffer > > Simple Parallel Decoder > > Sample Rate: 6.25 MS/s or 10 MS/s? > > Clock State: Rising Edge > > Voltage: 1.2 Volts, 1.8 Volts, or 3.3 Volts? > > Stop recording after 2 seconds > > Eric > > On Thursday, December 28, 2023 at 10:53:55 AM PST, > <bir...@soigeneris.com <mailto:bir...@soigeneris.com> > <mailto:bir...@soigeneris.com>> wrote: > > You can check each address line at the ROM to see they are all being > twiddled and that those connections are good. This is not fool proof as > a bad bus latch or any chip on the address bus can much up one of more > lines. > > The data lines are more complicated. If you test at the ROM you will see > them twiddling but you need to look at the ROM chip select at the same > time to make sure you are seeing data from the ROM. Then you need to > look for the same thing back at the processor to see if all the lines > are good back to there. > > If you have more than 8 channels on your LA it will be much, much > easier. As I recall I used channel 0 for the /WR had the Saelee software > filter out all data there that bit was not low. Then I had to guess at > what bit 0 might have actually been by looking at the disassembly. A lot > of work but I learned a lot on the process. > > Good luck, > > Jeff Birt > > *From:*M100 <m100-boun...@lists.bitchin100.com > <mailto:m100-boun...@lists.bitchin100.com> > <mailto:m100-boun...@lists.bitchin100.com>> *On Behalf Of *Eric > *Sent:* Thursday, December 28, 2023 12:00 PM > *To:* m...@bitchin100.com <mailto:m...@bitchin100.com> > <mailto:m...@bitchin100.com> > *Subject:* Re: [M100] Model 100 - LCD Shows Pixels Only > > Thank you everyone for the quick response! > > When I power up the computer, all pixels are on and remain dark (LCD is > entirely "black"). > > Contrast potentiometer: Seems to work as intended. The display will > lighten or darken as the potentiometer is adjusted. > > LCD PCB: No signs of corrosion and/or damaged traces. > > ROM: I'll ohm out the traces to see if I can find any broken > connections. Otherwise, are there any other troubleshooting steps I can > take? > > RAM: Jeff, great video! Thank you for sharing. The M100 Test Harness > sounds like an ideal tool. > > I have limited experience with a logic analyzer however it looks like a > fun challenge.I'll try to duplicate your setup but I may need some tips > on how to configure the Saleae software... > > Eric > > On Thursday, December 28, 2023 at 08:17:02 AM PST, Josh Malone > <josh.mal...@gmail.com <mailto:josh.mal...@gmail.com> <mailto:josh.mal...@gmail.com>> wrote: > -- bkw
