Getting started with SPI

RE: Getting started with SPI

haakonsh — Mon, 07 May 2018 09:06:35 GMT

Hey Payton,

I was convinced that we were talking about UART for some reason, but now I realize it's SPI.

We're gonna start by reading the status register:

uint16_t MOSI; //TX buffer
uint16_t MISO; //RX buffer

MOSI = 0b0101111111111111; //4 bits address (0x5) + 2 control bits (0x3=read) +    \
//10 bits data. 
//The data bits on MOSI are called the Over Read Character and is used to let the  \
//slave continue to send even though the master has sent want it needs for the     \
//current transfer. Most SPI slaves needs an ORC of 0xFF/0b11111111 to function    \
//properly.

//After the transfer is complete you need to extract the data bits out of MISO:
uint16_t DATA = MISO & 0b0000001111111111; // The mask of actual data bits. 

------------------------------------------------------------------------------------
To make things more readable you can do the following:
# define DATA_MSK 0b0000001111111111 
// Now you can extract the bits in a more human-readable form
uint16_t DATA = MISO & DATA_MSK;

More advanced:
#define WIPER0_ADDR 0x00 
#define TCON_ADDR   0x04
#define STATUS_ADDR 0x05

#define WRITE_CMD   0x00
#define INCR_CMD    0x01
#define DECR_CMD    0x02
#define READ_CMD    0x03

#define ADDR_POS    12
#define CMD_POS     10

uint16_t encode_tx_buffer(uint8_t addr, uint8_t cmd)
{
    return ((addr << ADDR_POS)|(cmd << CMD_POS) | DATA_MSK);
}
// To read the status register now:
uint16_t MOSI = encode_tx_buffer(STATUS_ADDR, READ_CMD); 
// Should be equal to 0b0101111111111111.

I wrote the code in this text editor so there might be some unwanted "features" present, just a heads-up.

Cheers,

Håkon.

RE: Getting started with SPI

Payton Grenich — Sun, 06 May 2018 19:11:28 GMT

Thanks for the response! No error is given because a variable in quotes is seen as a string and saved as ASCII in the register, similar to how "Nordic" is saved (apologies, I should have said "various issues" not "various errors"). Replacing "Nordic" with "0x80" in the code sends the ASCII 'version' of 0x80 on MOSI. ie, using a conversion tool, one can see that 0x80 is saved as 00110000 01111000 00111000 00110000 0001010. This binary value is exactly what is transmitted on MOSI, as I can see from using an oscilloscope. My issue is that some 8-bit binary values cannot be accessed by ASCII characters (eg, see binary values 10000000-10011111 on an extended ASCII table). So basically I need a way to save these and other values to static uint8_t m_tx_buf[] without using quotes and strings.

RE: Getting started with SPI

haakonsh — Fri, 04 May 2018 08:54:45 GMT

Hey Payton,

[quote user=""]I've tried modifying the value of TEST_STRING from "Nordic" to various hexadecimal formats such as 0x80, %80x, 0X80, "0x80", etc. but I get various errors when I try to do this.[/quote]

What error do you get when you replace "Nordic" with "0x80" ?

Also I suggest you try Segger Embedded Studio for any embedded development with our devices as we do not support Netbeans in our SDK.

Cheers,

Håkon.