Datasheet

PIC18FXX8
DS41159E-page 168 © 2006 Microchip Technology Inc.
17.4.6.1 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 8 bits at a time. After each byte is transmit-
ted, 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 con-
tains 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 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 transmitted.
Start and Stop conditions indicate the beginning and
end of transmission.
The Baud Rate Generator used for the SPI mode
operation is used to set the SCL clock frequency for
either 100 kHz, 400 kHz or 1 MHz I
2
C operation. See
Section 17.4.7 “Baud Rate Generator” for more
details.
A typical transmit sequence would go as follows:
1. The user generates a Start condition by setting
the Start Enable bit, SEN (SSPCON2<0>).
2. SSPIF is set. The MSSP module will wait the
required start time before any other operation
takes place.
3. The user loads the SSPBUF with the slave
address to transmit.
4. Address is shifted out the SDA pin until all 8 bits
are transmitted.
5. The MSSP module shifts in the ACK bit from the
slave device and writes its value into the
SSPCON2 register (SSPCON2<6>).
6. The MSSP module generates an interrupt at the
end of the ninth clock cycle by setting the SSPIF
bit.
7. The user loads the SSPBUF with eight bits of
data.
8. Data is shifted out the SDA pin until all 8 bits are
transmitted.
9. The MSSP module shifts in the ACK bit from the
slave device and writes its value into the
SSPCON2 register (SSPCON2<6>).
10. The MSSP module generates an interrupt at the
end of the ninth clock cycle by setting the SSPIF
bit.
11. The user generates a Stop condition by setting
the Stop Enable bit PEN (SSPCON2<2>).
12. Interrupt is generated once the Stop condition is
complete.