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, [email protected]
<[email protected]> wrote:
Eric,
Sent you a mail off list with a link to my capture files, etc.
Jeff
From: M100 <[email protected]> On Behalf Of Eric
Sent: Friday, December 29, 2023 2:00 AM
To: [email protected]
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, <[email protected]>
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 <[email protected]> On Behalf Of Eric
Sent: Thursday, December 28, 2023 12:00 PM
To: [email protected]
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
<[email protected]> wrote:
