PIC16F87X
9.2
MSSP I2C Operation
Two pins are used for data transfer. These are the SCL
pin, which is the clock, and the SDA pin, which is the
data. The SDA and SCL pins are automatically config-
ured when the I2C mode is enabled. The SSP module
functions are enabled by setting SSP Enable bit
SSPEN (SSPCON<5>).
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.
The MSSP module has six registers for I2C operation.
They are the:
• SSP Control Register (SSPCON)
• SSP Control Register2 (SSPCON2)
• SSP Status Register (SSPSTAT)
• Serial Receive/Transmit Buffer (SSPBUF)
• SSP Shift Register (SSPSR) - Not directly acces-
sible
Refer to Application Note AN578, "Use of the SSP
Module in the I 2C Multi-Master Environment."
A "glitch" filter is on the SCL and SDA pins when the pin
is an input. This filter operates in both the 100 kHz and
400 kHz modes. In the 100 kHz mode, when these pins
are an output, there is a slew rate control of the pin that
is independant of device frequency.
• 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:
FIGURE 9-5: I2C SLAVE MODE BLOCK
DIAGRAM
• I2C Slave mode (7-bit address)
Internal
Data Bus
• I2C Slave mode (10-bit address)
• I2C Master mode, clock = OSC/4 (SSPADD +1)
Read
Write
Before selecting any I2C mode, the SCL and SDA pins
must be programmed to inputs by setting the appropri-
ate TRIS bits. Selecting an I2C mode, by setting the
SSPEN bit, enables the SCL and SDA pins to be used
as the clock and data lines in I2C mode.
SSPBUF reg
SSPSR reg
SCL
SDA
Shift
Clock
The CKE bit (SSPSTAT<6:7>) sets the levels of the
SDA and SCL pins in either master or slave mode.
When CKE = 1, the levels will conform to the SMBUS
specification. When CKE = 0, the levels will conform to
the I2C specification.
MSb
LSb
Addr Match
Match detect
SSPADD reg
Set, Reset
S, P bits
(SSPSTAT reg)
Start and
Stop bit detect
1999 Microchip Technology Inc.
DS30292A-page 71
MICROCHIP [ MICROCHIP ]
