PIC16LF18854 Datasheet, PDF (473/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
31.4.9 ACKNOWLEDGE SEQUENCE
The 9th SCL pulse for any transferred byte in I²C is
dedicated as an Acknowledge. It allows receiving
devices to respond back to the transmitter by pulling
the SDA line low. The transmitter must release control
of the line during this time to shift in the response. The
Acknowledge (ACK) is an active-low signal, pulling the
SDA line low indicates to the transmitter that the
device has received the transmitted data and is ready
to receive more.
The result of an ACK is placed in the ACKSTAT bit of
the SSPxCON2 register.
Slave software, when the AHEN and DHEN bits are
set, allow the user to set the ACK value sent back to
the transmitter. The ACKDT bit of the SSPxCON2
register is set/cleared to determine the response.
Slave hardware will generate an ACK response if the
AHEN and DHEN bits of the SSPxCON3 register are
clear.
There are certain conditions where an ACK will not be
sent by the slave. If the BF bit of the SSPxSTAT regis-
ter or the SSPOV bit of the SSPxCON1 register are
set when a byte is received.
When the module is addressed, after the eighth falling
edge of SCL on the bus, the ACKTIM bit of the SSPx-
CON3 register is set. The ACKTIM bit indicates the
acknowledge time of the active bus. The ACKTIM Sta-
tus bit is only active when the AHEN bit or DHEN bit is
enabled.
31.5 I²C SLAVE MODE OPERATION
The MSSP Slave mode operates in one of four modes
selected by the SSPM bits of SSPxCON1 register. The
modes can be divided into 7-bit and 10-bit Addressing
mode. 10-bit Addressing modes operate the same as
7-bit with some additional overhead for handling the
larger addresses.
Modes with Start and Stop bit interrupts operate the
same as the other modes with SSPxIF additionally
getting set upon detection of a Start, Restart, or Stop
condition.
31.5.1 SLAVE MODE ADDRESSES
The SSPxADD register (Register 31-6) contains the
Slave mode address. The first byte received after a
Start or Restart condition is compared against the
value stored in this register. If the byte matches, the
value is loaded into the SSPxBUF register and an
interrupt is generated. If the value does not match, the
module goes idle and no indication is given to the
software that anything happened.
The SSP Mask register (Register 31-5) affects the
address matching process. See Section 31.5.9 “SSP
Mask Register” for more information.
31.5.1.1 I²C Slave 7-bit Addressing Mode
In 7-bit Addressing mode, the LSb of the received data
byte is ignored when determining if there is an address
match.
31.5.1.2 I²C Slave 10-bit Addressing Mode
In 10-bit Addressing mode, the first received byte is
compared to the binary value of ‘1 1 1 1 0 A9 A8 0’. A9
and A8 are the two MSb’s of the 10-bit address and
stored in bits 2 and 1 of the SSPxADD register.
After the acknowledge of the high byte the UA bit is set
and SCL is held low until the user updates SSPxADD
with the low address. The low address byte is clocked
in and all eight bits are compared to the low address
value in SSPxADD. Even if there is not an address
match; SSPxIF and UA are set, and SCL is held low
until SSPxADD is updated to receive a high byte
again. When SSPxADD is updated the UA bit is
cleared. This ensures the module is ready to receive
the high address byte on the next communication.
A high and low address match as a write request is
required at the start of all 10-bit addressing communi-
cation. A transmission can be initiated by issuing a
Restart once the slave is addressed, and clocking in
the high address with the R/W bit set. The slave
hardware will then acknowledge the read request and
prepare to clock out data. This is only valid for a slave
after it has received a complete high and low address
byte match.
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Preliminary
DS40001824A-page 473