SS pin and setup_spi()

LGU · Joined: 06 Apr 2009 Posts: 2

Hi

I can't get the SS1 pin to work together with the spi_write() function.

After running the program past the setup_spi() the SPI1CON1 reg show 0x003f. This means that the SSEN bit is clear and SS pin function is disabled. SPI1CON1 should be read 0x00BF after setup_spi().

Since there are a #define SPI_SS_DISABLED in the header file I then assume that SS pin function ought to be set by default. Data out and SCK works ok.

Regards
Lars

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Slave Select is a hardware input pin and only used on the Slave. On the Master you are free to choose any pin as a select output pin and drive it from your program, it will not be driven by the spi_write function.

LGU · Joined: 06 Apr 2009 Posts: 2

So it is !
I was reading the datasheet too quick. The description for the SS pin is like this " I/O pin , SPI1 slave synchronization or frame pulse I/O." The description is a bit vague, I assumed that slave sync was enabled even in master mode to sync external slaves.

SS pin is an output in SPI framed master mode but then the SCK is free running so it not much to use in my application. My application interface to an ENC28J60 that expect that SCK is low in idle.

SPI is a 4 pin interface so maybe SS pin should be active even in master mode!

Now I don't want to wait for the transmit to end so I need to use an interrupt to raise the pin.

Many thanks
Lars