Read-Write Operation

The TWI high-speed frame always begins with the following sequence:
  1. START condition (S)
  2. Host code (0000 1XXX)
  3. Not-acknowledge (NACK)

Note that to enable high-speed transfer, the client must send a NACK after receiving the host code.

As described previously, this sequence is sent at normal speed, and in case of multi-host, arbitration can only happen during this sequence.

Host codes are 8-bit reserved codes with the sole purpose of enabling High-Speed mode. Each host must use a different host code, which can be set through the FLEX_TWI_HSR.MCODE field.

Once this sequence has been sent, High-Speed mode is enabled and the host sends a repeated start to begin the programmed transfer. High-Speed mode remains enabled after repeated START (Sr) and only switches back to normal speed after a STOP condition (P).

Figure 8-116. High-Speed Mode Read-Write