I have been trying to understand some block diagrams in ATmega specs. Specifically, I am trying to figure out the meaning of some arrow heads in SPI block diagram of Atmega8. I see three arrows between SPI control and SPI status register (Figure 57. SPI Block Diagram, ATmega8 spec). Two arrows(SPIF and WCOL) are from SPI control to SPI status register, and one arrow(SPI2X) from SPI status register to SPI control. What do such arrows (arrow-heads) indicate in block diagrams? I see that all the three bits in the arrows (SPIF, WCOL and SPI2X) correspond to SPI Status Register "“ SPSR. Please let me know.