PIC16F72 Datasheet, PDF (50/136 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH MCU with A/D Converter

PIC16F72
9.3 SSP I²C Mode Operation
The SSP module in I²C mode fully implements all slave
functions, except general call support and provides
interrupts on START and STOP bits in hardware to
facilitate firmware implementations of the master func-
tions. The SSP module implements the Standard mode
specifications, as well as 7-bit and 10-bit addressing.
Two pins are used for data transfer. These are the RC3/
SCK/SCL pin, which is the clock (SCL), and the RC4/
SDI/SDA pin, which is the data (SDA). The user must
configure these pins as inputs or outputs through the
TRISC<4:3> bits.
The SSP module functions are enabled by setting SSP
Enable bit SSPEN (SSPCON<5>).
FIGURE 9-5:
SSP BLOCK DIAGRAM
(I²C MODE)
Read
Internal
Data Bus
Write
RC3/SCK/SCL
SSPBUF Reg
RC4/
SDI/
SDA
Shift
Clock
SSPSR Reg
MSb
LSb
Match Detect
Addr Match
SSPADD Reg
START and
Set, RESET
STOP Bit Detect
S, P Bits
(SSPSTAT Reg)
The SSP module has five registers for I²C operation:
• SSP Control Register (SSPCON)
• SSP Status Register (SSPSTAT)
• Serial Receive/Transmit Buffer (SSPBUF)
• SSP Shift Register (SSPSR) - Not directly
accessible
• SSP Address Register (SSPADD)
The SSPCON register allows control of the I²C opera-
tion. Four mode selection bits (SSPCON<3:0>) allow
one of the following I²C modes to be selected:
• I²C Slave mode (7-bit address)
• I²C Slave mode (10-bit address)
• I²C Slave mode (7-bit address), with START and
STOP bit interrupts enabled
• I²C Slave mode (10-bit address), with START and
STOP bit interrupts enabled
• I²C Firmware controlled Master operation, Slave
is IDLE
DS39597B-page 48
Selection of any I²C mode, with the SSPEN bit set,
forces the SCL and SDA pins to be open drain, pro-
vided these pins are programmed to inputs by setting
the appropriate TRISC bits.
Additional information on SSP I²C operation may be
found in the PICmicro™ Mid-Range MCU Reference
Manual (DS33023).
9.3.1 SLAVE MODE
In Slave mode, the SCL and SDA pins must be config-
ured as inputs (TRISC<4:3> set). The SSP module will
override the input state with the output data when
required (slave-transmitter).
When an address is matched or the data transfer after
an address match is received, the hardware automati-
cally will generate the Acknowledge (ACK) pulse, and
then load the SSPBUF register with the received value
currently in the SSPSR register.
Either or both of the following conditions will cause the
SSP module not to give this ACK pulse.
a) The buffer full bit BF (SSPSTAT<0>) was set
before the transfer was received.
b) The overflow bit SSPOV (SSPCON<6>) was set
before the transfer was received.
In this case, the SSPSR register value is not loaded
into the SSPBUF, but bit SSPIF (PIR1<3>) is set.
Table 9-2 shows what happens when a data transfer
byte is received, given the status of bits BF and
SSPOV. The shaded cells show the condition where
user software did not properly clear the overflow condi-
tion. Flag bit BF is cleared by reading the SSPBUF
register while bit SSPOV is cleared through software.
The SCL clock input must have a minimum high and
low for proper operation. The high and low times of the
I²C specification, as well as the requirement of the SSP
module are shown in timing parameter #100 and
parameter #101.
9.3.1.1 Addressing
Once the SSP module has been enabled, it waits for a
START condition to occur. Following the START condi-
tion, the eight bits are shifted into the SSPSR register.
All incoming bits are sampled with the rising edge of the
clock (SCL) line. The value of register SSPSR<7:1> is
compared to the value of the SSPADD register. The
address is compared on the falling edge of the eighth
clock (SCL) pulse. If the addresses match, and the BF
and SSPOV bits are clear, the following events occur:
a) The SSPSR register value is loaded into the
SSPBUF register.
b) The buffer full bit, BF is set.
c) An ACK pulse is generated.
d) SSP interrupt flag bit, SSPIF (PIR1<3>) is set
(interrupt is generated, if enabled) - on the falling
edge of the ninth SCL pulse.
 2002 Microchip Technology Inc.