I2C for PCF8574A

[awneil]

I am trying to use the Fastrack’s GPIO4&5 as a soft I2C bus to talk to a PCF8574A IO expander.

With no I2C device attached, adl_busSubscribe returns 0, and adl_busRead and adl_busWrite both return -31; ie, WM_BUS_NOT_CONNECTED_ON_I2C - which makes sense!

When I first attached my PCF8574A, with no pullups, I still got WM_BUS_NOT_CONNECTED_ON_I2C.
(the use of pullups is undocumented - see wavecom.com/modules/movie/sc … =4535#4535 )

So I added 1k pullups (to 3V), and now adl_busRead and adl_busWrite both return -1; ie, WM_BUS_MODE_UNKNOWN_TYPE - what does this indicate?

Using AT+WBR just returns “ERROR” - is there any way to get additional error details from this command?

Cross-Post: wavecom.com/modules/movie/sc … =5280#5280

[jan]

Hi awneil,

Have you checked the signal lines with an oscilloscope? I don’t know what the error means, but we had trouble communicating I2C on a Q2686. After looking on the scope it was obvious that the values for the pull-ups could be improved and after changing we got perfect communication on the bus.

Best Regards,
Jan

[awneil]

Doh!! I had SCL and SDA transposed in the bus suscription!

@jan

Have you checked the signal lines with an oscilloscope?

Yes - which confused me somewhat, as I couldn’t see any activity at all.
But I think the scope had got itself into some funny mode - that’s the trouble with this new-fangled digital stuff!

I don’t know what the error means

The documentation is no help, again!

In fact, the title to the table of error codes says, “Here are some numerical error codes” - does this mean that there’s also a whole buch of other error codes…?

[awneil]

@I

does this mean that there’s also a whole buch of other error codes…?

What a silly question - of course there are!

@wm_bus.h

/* Return values */
#define WM_BUS_PROC_DONE 0

#define WM_BUS_MODE_UNKNOWN_TYPE -1
#define WM_BUS_UNKNOWN_TYPE -11
#define WM_BUS_BAD_PARAMETER -12
#define WM_BUS_SPI1_ALREADY_USED -13
#define WM_BUS_I2C_HARD_ALREADY_USED -14
#define WM_BUS_I2C_SOFT_ALREADY_USED -15
#define WM_BUS_PARALLEL_ALREADY_USED -16

#define WM_BUS_UNKNOWN_HANDLE -21
#define WM_BUS_HANDLE_NOT_OPENED -22
#define WM_BUS_NO_MORE_HANDLE_FREE -23

#define WM_BUS_NOT_CONNECTED_ON_I2C -31
#define WM_BUS_NOT_ALLOWED_ADDRESS -32
#define WM_BUS_I2C_SOFT_GPIO_NOT_GPIO -33

#define WM_BUS_SPI_LCDEN_NOT_FREE -34
#define WM_BUS_SPI_AUX_NOT_FREE -35
#define WM_BUS_SPI_GPIO_CS_NOT_GPIO -36
#define WM_BUS_SPI_GPIO_CS_NOT_FREE -37

#define WM_BUS_PARALLEL_LCDEN_GPIO8_PB -38
#define WM_BUS_PARALLEL_CSUSER_GPIO_USED -39
#define WM_BUS_SPI_SPIEN_GPIO8_PB -40
#define WM_BUS_PARALLEL_LCDEN_PB -41
#define WM_BUS_SPI_CS_HARD_NOT_COHERENT -42

Basic Development Guide for Open-AT v3.12:

The table in section 3.9.2, “Returned Values Definition” omits all values after WM_BUS_SPI_GPIO_CS_NOT_FREE;

The table in section 3.9.7, “Error Codes (sic) Values” omits WM_BUS_I2C_HARD_ALREADY_USED, and all values after WM_BUS_SPI_GPIO_CS_NOT_FREE