mcp2515的问题
在读取mcp2515的寄存器和接受数据缓冲区的时候,为什么在写入地址之后还要往里面写入一个0xff呢?
uint8_t mcp2515_read_register(uint8_t adress)
{
uint8_t data;
/* CS low */
PORTB &= ~(1<<SPI_CS);
spi_putc(SPI_READ);
spi_putc(adress);
data = spi_putc(0xff);??
/* CS high */
PORTB |= (1<<SPI_CS);
return data;
}
uint8_t mcp2515_read_rx_buffer(uint8_t adress)
{
uint8_t data;
/* 躡erpr黤en ob die Adresse richtig ist */
if (adress & 0xF9)
return 0;
/* CS low */
PORTB &= ~(1<<SPI_CS);
spi_putc(SPI_READ_RX | adress);
data = spi_putc(0xff);??
/* CS high */
PORTB |= (1<<SPI_CS);
return data;