PIC18F23K22-ESLASHML datasheet(238/496 Pages) MICROCHIP

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PIC18(L)F2X/4XK22

DS41412C-page 238

Preliminary

 2010 Microchip Technology Inc.

15.6

I2C MASTER MODE

Master mode is enabled by setting and clearing the

appropriate SSPxM bits in the SSPxCON1 register and

by setting the SSPxEN bit. In Master mode, the SCLx

and SDAx lines are set as inputs and are manipulated

by the MSSPx 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 MSSPx module is disabled. Con-

trol of the I2C bus may be taken when the P bit is set,

or the bus is Idle.

In Firmware Controlled Master mode, user code

conducts all I2C 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 SDAx and SCLx lines.

The following events will cause the SSPx Interrupt Flag

bit, SSPxIF, to be set (SSPx interrupt, if enabled):

• Start condition detected

• Stop condition detected

• Data transfer byte transmitted/received

• Acknowledge transmitted/received

• Repeated Start generated

15.6.1

I2C 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 I2C bus will

not be released.

In Master Transmitter mode, serial data is output

through SDAx, while SCLx 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 the receive bit.

Serial data is received via SDAx, while SCLx 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.

A Baud Rate Generator is used to set the clock

frequency output on SCLx. See Section 15.7 “Baud

Rate Generator” for more detail.

Note 1: The MSSPx module, when configured in

I2C 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 SSPxBUF register

to initiate transmission before the Start

condition is complete. In this case, the

SSPxBUF will not be written to and the

WCOL bit will be set, indicating that a write

to the SSPxBUF did not occur

2: When

Master

mode,

Start/Stop

detection is masked and an interrupt is

generated when the SEN/PEN bit is

cleared and the generation is complete.

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