I own a PIC18F4550 and I need to make him a slave in the SPI model, but I'm not understanding the SSPBUF register. According to the datasheet, it is a Serial Receive / Transmit Buffer Register (SSPBUF). But how do I know he's with the information or sending information through it? I do programming in C ont the MPLAB x.
http://ww1.microchip.com/downloads/en/DeviceDoc/39632e.pdf
Hi Odivio,
I've never worked with this kind of registers, but after a brief overview of the datasheet, I think it's allways shifting data into (SDI) and out (SDO) of the Shift Register (SSPSR) and you can transfer data from SSPSR to SSPBUF (for reading operation) whenever you want (count clock ticks to not re-load any bit of data), or transfer from SSPBUF to SSPSR (for writing operation).
- Since it is always shifting data in and out, when Master sends "relevant" data, it is also shifting in (both through SSPSR) but "your software" has to ignore input (SDI).
- Slave has to wait until all those 8-bits are shifted in (SDI) before to transfer then to SSPBUF, it will be also shifting data out through SDO but Master won't care at this moment.
Configure SDI, SDO, SCK, clear picture on "Figure 19-2: SPI MASTER/SLAVE CONNECTION" and interesting data around page 200.
Also check that interrupts and status bits have to be appropriately set to allow you to know by these flags when a full new byte has been shifted in/out, etc...
The SSPBUF register is ony used to transfer or receive data through the SPI. To transfer a byte data, it first place inside the SSPBUF register.
SSPCON1 is the register use to select slave or master mode.
To make the pic SPI slave you have to use SSPM3:SSPM0 (lower 4 bit) of SSPCON1 register. for example to to use the SPI as slave mode use SSPCON1=0b00000100;
Read page 201 on the datasheet for more infomation
- Badges
- Science topic
- Similar topics
- Computer Science and Engineering
- Programming Languages