7-bit Transmission

A master device can transmit a read request to a slave, and then clock data out of the slave. The list below outlines what software for a slave will need to do to accomplish a standard transmission. Figure 1 can be used as a reference to this list.

  1. 1.Master sends a Start condition on SDA and SCL.
  2. 2.S bit is set; SSPxIF is set if interrupt on Start detect is enabled.
  3. 3.Matching address with R/W bit set is received by the Slave setting SSPxIF bit.
  4. 4.Slave hardware generates an ACK and sets SSPxIF.
  5. 5.SSPxIF bit is cleared by user.
  6. 6.Software reads the received address from SSPxBUF, clearing BF.
  7. 7.R/W is set so CKP was automatically cleared after the ACK.
  8. 8.The slave software loads the transmit data into SSPxBUF.
  9. 9.CKP bit is set releasing SCL, allowing the master to clock the data out of the slave.
  10. 10.SSPxIF is set after the ACK response from the master is loaded into the ACKSTAT register.
  11. 11.SSPxIF bit is cleared.
  12. 12.The slave software checks the ACKSTAT bit to see if the master wants to clock out more data.
    1. 1.If the master ACKs then the clock will be stretched.
    2. 2.ACKSTAT is the only bit updated on the rising edge of the ninth SCL clock instead of the falling edge.
  13. 13.Steps 9-13 are repeated for each transmitted byte.
  14. 14.If the master sends a not ACK; the clock is not held, but SSPxIF is still set.
  15. 15.The master sends a Restart condition or a Stop.
  16. 16.The slave is no longer addressed.
Figure 1. I2C Slave, 7-bit Address, Transmission (AHEN = 0)