Datasheet

 2010-2012 Microchip Technology Inc. DS41419D-page 275
PIC16(L)F1824/1828
25.6 I
2
C Master Mode
Master mode is enabled by setting and clearing the
appropriate SSP1M bits in the SSP1CON1 register and
by setting the SSP1EN bit. In Master mode, the SCL
and SDA lines are set as inputs and are manipulated by
the MSSP1 hardware.
Master mode of operation is supported by interrupt
generation on the detection of the Start and Stop con-
ditions. The Stop (P) and Start (S) bits are cleared from
a Reset or when the MSSP1 module is disabled. Con-
trol of the I
2
C bus may be taken when the P bit is set,
or the bus is Idle.
In Firmware Controlled Master mode, user code
conducts all I
2
C bus operations based on Start and
Stop bit condition detection. Start and Stop condition
detection is the only active circuitry in this mode. All
other communication is done by the user software
directly manipulating the SDA and SCL lines.
The following events will cause the SSP1 Interrupt Flag
bit, SSP1IF, to be set (SSP1 interrupt, if enabled):
• Start condition detected
• Stop condition detected
• Data transfer byte transmitted/received
• Acknowledge transmitted/received
• Repeated Start generated
25.6.1 I
2
C MASTER MODE OPERATION
The master device generates all of the serial clock
pulses and the Start and Stop conditions. A transfer is
ended with a Stop condition or with a Repeated Start
condition. Since the Repeated Start condition is also
the beginning of the next serial transfer, the I
2
C bus will
not be released.
In Master Transmitter mode, serial data is output
through SDA, while SCL outputs the serial clock. The
first byte transmitted contains the slave address of the
receiving device (7 bits) and the Read/Write
(R/W) bit.
In this case, the R/W
bit will be logic ‘0’. Serial data is
transmitted eight bits at a time. After each byte is trans-
mitted, an Acknowledge bit is received. Start and Stop
conditions are output to indicate the beginning and the
end of a serial transfer.
In Master Receive mode, the first byte transmitted
contains the slave address of the transmitting device
(7 bits) and the R/W
bit. In this case, the R/W bit will be
logic ‘1’. Thus, the first byte transmitted is a 7-bit slave
address followed by a ‘1’ to indicate the receive bit.
Serial data is received via SDA, while SCL outputs the
serial clock. Serial data is received 8 bits at a time. After
each byte is received, an Acknowledge bit is transmit-
ted. Start and Stop conditions indicate the beginning
and end of transmission.
A Baud Rate Generator is used to set the clock
frequency output on SCL. See Section 25.7 “Baud
Rate Generator” for more detail.
Note 1: The MSSP1 module, when configured in
I
2
C Master mode, does not allow queue-
ing of events. For instance, the user is not
allowed to initiate a Start condition and
immediately write the SSP1BUF register
to initiate transmission before the Start
condition is complete. In this case, the
SSP1BUF will not be written to and the
WCOL bit will be set, indicating that a
write to the SSP1BUF did not occur
2: When in Master mode, Start/Stop
detection is masked and an interrupt is
generated when the SEN/PEN bit is
cleared and the generation is complete.