Datasheet

PIC16(L)F1938/9
DS40001574C-page 258  2011-2013 Microchip Technology Inc.
24.5.3.3 7-bit Transmission with Address
Hold Enabled
Setting the AHEN bit of the SSPCON3 register
enables additional clock stretching and interrupt
generation after the eighth falling edge of a received
matching address. Once a matching address has
been clocked in, CKP is cleared and the SSPIF
interrupt is set.
Figure 24-19
displays a standard waveform of a 7-bit
Address Slave Transmission with AHEN enabled.
1. Bus starts Idle.
2. Master sends Start condition; the S bit of
SSPSTAT is set; SSPIF is set if interrupt on Start
detect is enabled.
3. Master sends matching address with R/W
bit
set. After the eighth falling edge of the SCL line
the CKP bit is cleared and SSPIF interrupt is
generated.
4. Slave software clears SSPIF.
5. Slave software reads ACKTIM bit of SSPCON3
register, and R/W
and D/A of the SSPSTAT reg-
ister to determine the source of the interrupt.
6. Slave reads the address value from the
SSPBUF register clearing the BF bit.
7. Slave software decides from this information if it
wishes to ACK
or not ACK and sets ACKDT bit
of the SSPCON2 register accordingly.
8. Slave sets the CKP bit releasing SCL.
9. Master clocks in the ACK
value from the slave.
10. Slave hardware automatically clears the CKP bit
and sets SSPIF after the ACK
if the R/W bit is
set.
11. Slave software clears SSPIF.
12. Slave loads value to transmit to the master into
SSPBUF setting the BF bit.
13. Slave sets CKP bit releasing the clock.
14. Master clocks out the data from the slave and
sends an ACK
value on the ninth SCL pulse.
15. Slave hardware copies the ACK
value into the
ACKSTAT bit of the SSPCON2 register.
16. Steps 10-15 are repeated for each byte transmit-
ted to the master from the slave.
17. If the master sends a not ACK
the slave
releases the bus allowing the master to send a
Stop and end the communication.
Note: SSPBUF cannot be loaded until after the
ACK.
Note: Master must send a not ACK on the last byte
to ensure that the slave releases the SCL
line to receive a Stop.