Electronics > Microcontrollers

Need help dumping the ROM in a failing 80C49 (MCS-48)

<< < (9/11) > >>

trondl:

--- Quote from: james_s on December 20, 2021, 10:23:15 pm ---The chip getting "ouch hot" is a very bad sign, that should never be happening. Do you perhaps get the polarity wrong and connect +5V from your PSU to Vss instead of Vcc? Did you connect the - output from the PSU to the +5V rail on the board instead of ground, resulting in +10V across the IC? I agree that a second opinion here would be useful, or at least a schematic showing visually how you have tried to hook it up each time.

--- End quote ---

I always doublecheck such things. If tiered, triplecheck.
Positive to pin 40/VCC with the pin bent out of socket, and negative to arduino shield ground which VSS is tied to.
I believe that there has been an internal short or lose wire that was remedied by freezing.
The psu in the intended unit was probably not strong enough to heat up the chip, same with the arduino shield.
30mA at 5V would be a rather low resistance, but no direct short.

Another round of freezing temperatures (-10C) is inbound here in Norway.
I’ll give it a second chance, or I’ll toss it in the oven at 150C for some minutes as a last resort.

trondl:
Sorry for the very late sitrep.
I had to put it aside to continue on some other projects.

Thought it was about time to see if something could be done again.
And something was observed!

I thought it was about time I did some of the most sane thing to to: compare the waveforms to a working 8749.
This time without a separate PSU for VCC, and in room temperature.

When idle, 8749 gets a clean 5V at the i/o bus and 0V at VCC.
8049 only get about 1.5V at the bus and VCC / VDD is about 1V.

When dumping (with the standard unmodified hex file loaded in the shield), the waveforms on the 8749 are stable with clean pulses and has a distinct beginning and end pulsing of the data stream.
The 8049 on the other hand has a very unstable and fast switching stream, as in hi-lo-hi-lo-hi-lo in the time frame the 8749 would only go hi-lo,  and as previously mentioned, "floating" areas of the stream at about 1-2V.

I still get the same semi-random values as before the "ouch" moment with the external psu.

Something seems very wrong here and may explain why I get no valid data.

With a DMM I tried to check if there was a resistance between VSS and the i/o pins, VCC and most of the readings where in the mega ohms if at all, compared to the 8749 in kilo ohms.
Could this indicate that the chip is indeed very dead and is no longer worth the time, considering that I still get the same "values" as before?

trondl:
One further observation is that I see in the schematics that there are no pull-up or down resistors on the data bus D0 to D7 (AD0 - AD7).
It's all directly routed to the Arduino.
Could this be an issue?
The "floating" area of the stream may actually be Low bits, but not low enough in voltage (1.5V).
Also the additional address pins P20 to P23 (A8 to A11) all give perfect pulses.

Andy Watson:
What are you doing with the PROG pin? Looking at an old datasheet for the Intel 8048/9 series there is a curious note under the programing and verify timing waveforms for the 8048 (I can't see an equivalent for th 8049 - so YMMV), it says:
"Prog must float if EA is low, or if T0=5V for the 8748. For the 8048 PROG must always float."

trondl:
Hi again!
Got some update, although not the best kind of update.
Bought an almost cheap second unit from japan in the hope that dumping the second MCU would be a breeze.
Not so.
The dumping waveforms are almost exactly like the failing one.
It just seems like the LO bits never reach ~0V and VCC is also idle at 1.5V, just as the Data pins are doing.

Is this actually a fault on the Arduino or the code?
The Data pins on the shield are directly connected to the Arduino without any pull-up or down resistors (unsure about what to do when trying to help a signal go LO).

I've seen articles about a built in pull-up resistor in the Arduino itself.
Could this be utilized, if not already in the code (if so, where?)

Included screendumps from the DSO:
First: "new" 8049 during a dump on pin D7, second: VCC idle, third: working 8749 during dump, 8749 VCC idle.


--- Quote from: Andy Watson on February 05, 2022, 03:08:18 pm ---What are you doing with the PROG pin? Looking at an old datasheet for the Intel 8048/9 series there is a curious note under the programing and verify timing waveforms for the 8048 (I can't see an equivalent for th 8049 - so YMMV), it says:
"Prog must float if EA is low, or if T0=5V for the 8748. For the 8048 PROG must always float."

--- End quote ---
PROG is HI during the entire dump

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version