Address SPI Communication Problem on ATMega2560 #38
Conversation
When using the Arduino Mega platform with the W5500 shield, there is contention between the LED signal and the SCK signal. On the Mega, the LED is mapped to digital pin 13. On the Uno, 13 is the SCK signal, but on the Mega these signals are routed to different headers altogether. The shield still works in sketches because the SPI signals are also routed to the ISCP header, which is connected to the shield. The logic in the bootloader is that if the SCK pin and LED pin definitions don't match, the LED pin will be initialized and will blink in the bootloader's main polling loop. On the Mega 2560, the SCK pin definition and LED pin definition _do not match_, meaning this logic was included. Because of the routing of the signals, LED pin (Digital 13) and SCK are actually shorted together, so blinking the LED is causing contention on the SCK line. For now, LED blinking is disabled on the ATMega2560. With this change, we can successfully upload binaries to the device over Ethernet.
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@phillipjohnston why do you think there is contention between the LED and the SCK on ATMega2560? I actually have a setup with W5500 shield who work with a blinking LED. The problem you experience is actually in the W5500. switch the LED off will just solve the bootloader contention, if your sketch will use pin 11/12/13 you will have again the same problem. http://wizwiki.net/wiki/doku.php?id=osh:w5500_ethernet_shield:start
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Hi @hagaigold, You answered the question with your answer. I did not perform (or notice) the necessary rework to eliminate the contention. |
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I understand your perspective and appreciate receiving your input. I made the fix with the information I had available to me at the time. None of us is perfect.
Cheers,
Phillip
… On 29Jun2020, at 13:10, Hagai Gold ***@***.***> wrote:
I wan not asking a "real" question ;)
your fix to the code suggests there is a problem in the code, while I don't think there is.
W5500 shield should be configured correctly if you use it on the Mega board, and want to use pin D11/12/13 (which the bootloader does).
I put this information with the hope others can befit from it.
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When using the Arduino Mega platform with the W5500 shield, there is contention between the LED signal and the SCK signal. On the Mega, the LED is mapped to digital pin 13. On the Uno, 13 is the SCK signal, but on the Mega these signals are routed to different headers altogether.
The shield still works in sketches because the SPI signals are also routed to the ISCP header, which is connected to the shield.
The logic in the bootloader is that if the SCK pin and LED pin definitions don't match, the LED pin will be initialized and will blink in the bootloader's main polling loop. On the Mega 2560, the SCK pin definition and LED pin definition do not match, meaning this logic was included.
Because of the routing of the signals, LED pin (Digital 13) and SCK are actually shorted together, so blinking the LED is causing contention on the SCK line.
For now, LED blinking is disabled on the ATMega2560. With this change, we can successfully upload binaries to the device over Ethernet.
Fixes #37