PIC18FXX20
Note: The MSSP Module, when configured in I2C
Master mode, does not allow queueing of
events. For instance, the user is not
allowed to initiate a START condition and
immediately write the SSPBUF register to
initiate transmission before the START
condition is complete. In this case, the
SSPBUF will not be written to and the
WCOL bit will be set, indicating that a write
to the SSPBUF did not occur.
17.4.6
MASTER MODE
Master mode is enabled by setting and clearing the
appropriate SSPM bits in SSPCON1 and by setting the
SSPEN bit. In Master mode, the SCL and SDA lines
are manipulated by the MSSP hardware.
Master mode of operation is supported by interrupt
generation on the detection of the START and STOP
conditions. The STOP (P) and START (S) bits are
cleared from a RESET, or when the MSSP module is
disabled. Control of the I2C bus may be taken when the
P bit is set or the bus is IDLE, with both the S and P bits
clear.
The following events will cause SSP interrupt flag bit,
SSPIF, to be set (SSP interrupt if enabled):
• START condition
In Firmware Controlled Master mode, user code con-
ducts all I2C bus operations based on START and
STOP bit conditions.
• STOP condition
Once Master mode is enabled, the user has six
options.
1. Assert a START condition on SDA and SCL.
• Data transfer byte transmitted/received
• Acknowledge Transmit
• Repeated START
2. Assert a Repeated START condition on SDA
and SCL.
3. Write to the SSPBUF register initiating
transmission of data/address.
4. Configure the I2C port to receive data.
5. Generate an Acknowledge condition at the end
of a received byte of data.
6. Generate a STOP condition on SDA and SCL.
2
FIGURE 17-16:
MSSP BLOCK DIAGRAM (I C MASTER MODE)
Internal
SSPM3:SSPM0
SSPADD<6:0>
Data Bus
Read
Write
SSPBUF
SSPSR
Baud
Rate
Generator
SDA
SCL
Shift
Clock
SDA In
MSb
LSb
START bit, STOP bit,
Acknowledge
Generate
START bit Detect
STOP bit Detect
SCL In
Bus Collision
Set/Reset, S, P, WCOL (SSPSTAT)
Write Collision Detect
Clock Arbitration
State Counter for
end of XMIT/RCV
Set SSPIF, BCLIF
Reset ACKSTAT, PEN (SSPCON2)
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 181
MICROCHIP [ MICROCHIP ]
