PIC16F87XA
2
9.4.1
REGISTERS
9.4
I C Mode
The MSSP module has six registers for I2C operation.
These are:
The MSSP module in I2C mode fully implements all
master and slave functions (including general call sup-
port) and provides interrupts on START and STOP bits
in hardware to determine a free bus (multi-master func-
tion). The MSSP module implements the standard
mode specifications, as well as 7-bit and 10-bit
addressing.
• MSSP Control Register (SSPCON)
• MSSP Control Register 2 (SSPCON2)
• MSSP Status Register (SSPSTAT)
• Serial Receive/Transmit Buffer (SSPBUF)
• MSSP Shift Register (SSPSR) - Not directly
accessible
Two pins are used for data transfer:
• Serial clock (SCL) - RC3/SCK/SCL
• Serial data (SDA) - RC4/SDI/SDA
• MSSP Address Register (SSPADD)
SSPCON, SSPCON2 and SSPSTAT are the control
and status registers in I2C mode operation. The
SSPCON and SSPCON2 registers are readable and
writable. The lower 6 bits of the SSPSTAT are read
only. The upper two bits of the SSPSTAT are read/
write.
The user must configure these pins as inputs or outputs
through the TRISC<4:3> bits.
FIGURE 9-7:
MSSP BLOCK DIAGRAM
(I2C MODE)
SSPSR is the shift register used for shifting data in or
out. SSPBUF is the buffer register to which data bytes
are written to or read from.
Internal
Data Bus
Read
Write
SSPADD register holds the slave device address
when the SSP is configured in I2C Slave mode. When
the SSP is configured in Master mode, the lower
seven bits of SSPADD act as the baud rate generator
reload value.
SSPBUF reg
RC3/SCK/SCL
Shift
Clock
In receive operations, SSPSR and SSPBUF together
create a double buffered receiver. When SSPSR
receives a complete byte, it is transferred to SSPBUF
and the SSPIF interrupt is set.
SSPSR reg
RC4/
SDI/
SDA
MSb
LSb
Addr Match
Match Detect
During transmission, the SSPBUF is not double buff-
ered. A write to SSPBUF will write to both SSPBUF and
SSPSR.
SSPADD reg
START and
Set, Reset
S, P bits
(SSPSTAT reg)
STOP bit Detect
DS39582A-page 78
AdvanceInformation
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
