Datasheet

PIC16(L)F1526/7
DS41458C-page 216  2011-2013 Microchip Technology Inc.
21.5.2 SLAVE RECEPTION
When the R/W
bit of a matching received address byte
is clear, the R/W
bit of the SSPxSTAT register is
cleared. The received address is loaded into the
SSPxBUF register and acknowledged.
When the overflow condition exists for a received
address, then not Acknowledge is given. An overflow
condition is defined as either bit BF of the SSPxSTAT
register is set, or bit SSPOV of the SSPxCON1 register
is set. The BOEN bit of the SSPxCON3 register
modifies this operation. For more information see
Register 21-4.
An MSSPx interrupt is generated for each transferred
data byte. Flag bit, SSPxIF, must be cleared by
software.
When the SEN bit of the SSPxCON2 register is set,
SCLx will be held low (clock stretch) following each
received byte. The clock must be released by setting
the CKP bit of the SSPxCON1 register, except
sometimes in 10-bit mode. See
Section 21.2.3 “SPI
Master Mode”
for more detail.
21.5.2.1 7-bit Addressing Reception
This section describes a standard sequence of events
for the MSSPx module configured as an I
2
C slave in
7-bit Addressing mode. Figure 21-14 and Figure 21-15
is used as a visual reference for this description.
This is a step by step process of what typically must
be done to accomplish I
2
C communication.
1. Start bit detected.
2. S bit of SSPxSTAT is set; SSPxIF is set if
interrupt on Start detect is enabled.
3. Matching address with R/W
bit clear is received.
4. The slave pulls SDAx low sending an ACK
to the
master, and sets SSPxIF bit.
5. Software clears the SSPxIF bit.
6. Software reads received address from
SSPxBUF clearing the BF flag.
7. If SEN = 1; Slave software sets CKP bit to
release the SCLx line.
8. The master clocks out a data byte.
9. Slave drives SDAx low sending an ACK
to the
master, and sets SSPxIF bit.
10. Software clears SSPxIF.
11. Software reads the received byte from
SSPxBUF clearing BF.
12. Steps 8-12 are repeated for all received bytes
from the master.
13. Master sends Stop condition, setting P bit of
SSPxSTAT, and the bus goes idle.
21.5.2.2 7-bit Reception with AHEN and DHEN
Slave device reception with AHEN and DHEN set
operate the same as without these options with extra
interrupts and clock stretching added after the 8th fall-
ing edge of SCLx. These additional interrupts allow the
slave software to decide whether it wants to ACK
the
receive address or data byte, rather than the hard-
ware. This functionality adds support for PMBus™ that
was not present on previous versions of this module.
This list describes the steps that need to be taken by
slave software to use these options for I
2
C communi-
cation. Figure 21-16 displays a module using both
address and data holding. Figure 21-17 includes the
operation with the SEN bit of the SSPxCON2 register
set.
1. S bit of SSPxSTAT is set; SSPxIF is set if
interrupt on Start detect is enabled.
2. Matching address with R/W
bit clear is clocked
in. SSPxIF is set and CKP cleared after the 8th
falling edge of SCLx.
3. Slave clears the SSPxIF.
4. Slave can look at the ACKTIM bit of the
SSPxCON3 register to determine if the SSPxIF
was after or before the ACK.
5. Slave reads the address value from SSPxBUF,
clearing the BF flag.
6. Slave sets ACK
value clocked out to the master
by setting ACKDT.
7. Slave releases the clock by setting CKP.
8. SSPxIF is set after an ACK
, not after a NACK.
9. If SEN = 1 the slave hardware will stretch the
clock after the ACK.
10. Slave clears SSPxIF.
11. SSPxIF set and CKP cleared after 8th falling
edge of SCLx for a received data byte.
12. Slave looks at ACKTIM bit of SSPxCON3 to
determine the source of the interrupt.
13. Slave reads the received data from SSPxBUF
clearing BF.
14. Steps 7-14 are the same for each received data
byte.
15. Communication is ended by either the slave
sending an ACK
= 1, or the master sending a
Stop condition. If a Stop is sent and Interrupt on
Stop Detect is disabled, the slave will only know
by polling the P bit of the SSTSTAT register.
Note: SSPxIF is still set after the 9th falling edge of
SCLx even if there is no clock stretching and
BF has been cleared. Only if NACK is sent
to master is SSPxIF not set