OLED driver works at 32 MHz but not at 64 MHz

[Ttelmah]

Just as a FYI, I've put together a 46K80, and done a basic software I2C test to a device on the bench here. Runs fine at both 32MHz, and 64Mhz. At 64, the clock timing was about 1% faster than at 32MHz, but still just under 100K.
The library is fine (5.075).
However I can make it hang, if the RB7 line does not go high properly.

[johanpret]

Compiler version Latest - 5.075

Tried with older versions as well same result.
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Johan Pretorius

[Ttelmah]

So back to the questions we have already asked about your hardware.

[johanpret]

I use 2k pullup to 3V3. Let me flash LED in main loop. Now on timer interrupt.
This is making me crazy, He He.
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Johan Pretorius

[johanpret]

Maybe I must move pullup closer to OLED. Now connected with 4 wires about 20cm Long. I will look at shortening the wires.
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Johan Pretorius

[Ttelmah]

2K is 'upper end' of the range for 3.3v, but should be OK at 100K.
However the big questions are about the decoupling and supplies to the chip.

[johanpret]

Let me decrease the resistance to 1K5. I'll give feedback.
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Johan Pretorius

[johanpret]

I have 100nF decouling close to each chip on the board. The display has no decoupling maybe I can add cap on the power pins on the display.
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Johan Pretorius

[johanpret]

Really does not make sense. I lowered the resistors to 1K5 I added extra capacitors and I remover the 20cm cable. Same result, work with 32MHz and not with 64MHz. Also checked with LED in main loop program is running.
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Johan Pretorius

[Ttelmah]

The chip requires at least two such capacitors, _and_ a 10uF low ESR capacitor on the Vcap pin. This latter is vital. The chip runs internally on only about 1.8v, and this capacitor stabilises the regulator that feeds the core.

[johanpret]

Have 10uF on Vcap for pic and 1 x 100nF and 1 x 1uF
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Johan Pretorius

[johanpret]

I will try on different pic PIC18F26K40 and Pic18F67K22.
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Johan Pretorius

[Ttelmah]

[dyeatman]

The question was asked early on to verify the chip is actually running at 64mhz but I didn't see an answer.... is it confirmed to be at 64mhz with the led/scope test?
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[Ttelmah]

Agreed.
This should be the first test.
However I've seen these chips work OK, for a really basic test, and then go screwy, when you actually run more complex code.
Something like an LED flasher, together with a simple serial send/receive, and I'd start to be happy...