WIZnet Developer Forum

MISO is always high

I am using an external W5100 with Arduino Uno board. Arduino sources 3.3V to the chip. The Arduino seems to output SCLK, /SCS, and MOSI properly. But the returned MISO is always high (3.3V), with noise at the same frequency as SCLK (4MHz). When I try connecting this Arduino to WIZ811MJ instead, all 4 signals are fine and communication is successful.

The external W5100 circuitry is an exact copy of WIZ811MJ. SPI_EN is an inverse of /SCS. OPMODE is 000.
I leave /CS and /RESET floated. Is this okay? A’s and D’s pin are all floated as well.

I though the chip wasn’t selected so I tried forcing /SCS to GND but it doesn’t seem to solve anything (is doing this acceptable since there is only one slave?)

Here is how the signal looks like. Both signals weren’t captured at the same instant of time. Blue is MISO. Orange is MOSI, despite the label on the scope.


I think it is reset problem.
You should control reset. The timing is in datasheet.

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