1997 Microchip Technology Inc.
DS30444E - page 73
PIC16C9XX
11.3
SSP I2C 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
rmware implementations of the master functions. The
SSP module implements the standard mode specica-
tions 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 congure
these
pins
as
inputs
or
outputs
through
the
TRISC<4:3> bits. The SSP module functions are
enabled by setting SSP Enable bit SSPEN (SSP-
CON<5>).
FIGURE 11-18: SSP BLOCK DIAGRAM
(I2C MODE)
The SSP module has ve registers for I2C operation.
These are the:
SSP Control Register (SSPCON)
SSP Status Register (SSPSTAT)
Serial Receive/Transmit Buffer (SSPBUF)
SSP Shift Register (SSPSR) - Not directly acces-
sible
SSP Address Register (SSPADD)
Read
Write
SSPSR reg
Match detect
SSPADD reg
Start and
Stop bit detect
SSPBUF reg
Internal
data bus
Addr Match
Set, Reset
S, P bits
(SSPSTAT reg)
RC3/SCK/SCL
RC4/
shift
clock
MSb
SDI/
LSb
SDA
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 Mode, slave is
idle
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.
The SSPSTAT register gives the status of the data
transfer. This information includes detection of a START
or STOP bit, species if the received byte was data or
address if the next byte is the completion of 10-bit
address, and if this will be a read or write data transfer.
The SSPSTAT register is read only.
The SSPBUF is the register to which transfer data is
written to or read from. The SSPSR register shifts the
data in or out of the device. In receive operations, the
SSPBUF and SSPSR create a doubled buffered
receiver. This allows reception of the next byte to begin
before reading the last byte of received data. When the
complete byte is received, it is transferred to the
SSPBUF register and ag bit SSPIF is set. If another
complete byte is received before the SSPBUF register
is read, a receiver overow has occurred and bit
SSPOV (SSPCON<6>) is set and the byte in the
SSPSR is lost.
The SSPADD register holds the slave address. In 10-bit
mode, the user needs to write the high byte of the
address (1111 0 A9 A8 0). Following the high byte
address match, the low byte of the address needs to be
loaded (A7:A0).