PIC18FXX20
17.4.6.1
I2C Master Mode Operation
A typical transmit sequence would go as follows:
1. The user generates a START condition by set-
The master device generates all of the serial clock
pulses and the START and STOP conditions. A trans-
fer is ended with a STOP condition or with a Repeated
START condition. Since the Repeated START condi-
tion is also the beginning of the next serial transfer, the
I2C bus will not be released.
ting
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
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.
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.
The baud rate generator used for the SPI mode opera-
tion is used to set the SCL clock frequency for either
100 kHz, 400 kHz or 1 MHz I2C operation. See
Section 17.4.7 (“Baud Rate Generator”), for more
detail.
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.
DS39609A-page 182
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2003 Microchip Technology Inc.
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