ST95HF on MISO

noor · ‎2017-07-07

Posted on July 07, 2017 at 16:09

Hi,

I am designed a board with ST95HF on it. I tried to communicate with the sensor using aardvark programmer SPI but there is no activity on the MISO line at all. I have been trying the echo command which is just sending 55 from my understanding and reads back 00 even though MISO line stays high all the time. I am not a software person so I am not sure what's wrong.

Kind regards,

Noor

Peter Boringer · ‎2017-07-10

Posted on July 10, 2017 at 15:23

Hello Noor,

Did you check the pins 19 and 20 of the ST95HF respectively SSI_0 and SSI_1. They should be set to VCC via a resistor for SSI_0 and GND via a resistor for SSI_1 (1 KOhms for example). In the specification it is also mention that the MISO, MOSI and SPI_SS has to be connected not left open. After that at least the 95HF might be able to answer to the echo command.

Else can you provide the schematics to check the ST95HF connections

Thanks

noor · ‎2017-07-10

Posted on July 10, 2017 at 15:49

Thank you for your reply. This is the schematic for my design. I have pulled the SSI_0 high and SSI_1 low.

Peter Boringer · ‎2017-07-10

Posted on July 10, 2017 at 16:32

Hi Noor,

Schematic sounds good.

Why did you add a serial resistor of 22ohms on MISO?

Did you generate after power up a negative pulse of 10 us minimum on IRQ_IN pin 12 as described on the specification paragraph Startup sequence

Else do you check that SPI_SS in low during SPI exchange? And verify that the transfer is MSB first?. If all is done the echo command should work.

Regards