Microchip Technology MA300015 Data Sheet

© 2011 Microchip Technology Inc.

DS70150E-page 115

The I

2

C module generates two interrupt flags, MI2CIF

(I

2

C Master Interrupt Flag) and SI2CIF (I

2

C Slave Inter-

rupt Flag). The MI2CIF interrupt flag is activated on
completion of a master message event. The SI2CIF
interrupt flag is activated on detection of a message
directed to the slave. 

The I

2

C standard requires slope control on the SDA

and SCL signals for Fast Mode (400 kHz). The control
bit, DISSLW, enables the user to disable slew rate con-
trol, if desired. It is necessary to disable the slew rate
control for 1 MHz mode.

The control bit, IPMIEN, enables the module to support
Intelligent Peripheral Management Interface (IPMI).
When this bit is set, the module accepts and acts upon
all addresses. 

The general call address can address all devices. When
this address is used, all devices should, in theory,
respond with an acknowledgement.

The general call address is one of eight addresses
reserved for specific purposes by the I

2

C protocol. It

consists of all ‘0’s with R_W = 0.

The general call address is recognized when the Gen-
eral Call Enable bit (GCEN) is set (I2CCON<7> = 1).
Following a Start bit detection, 8 bits are shifted into
I2CRSR and the address is compared with I2CADD,
and is also compared with the general call address
which is fixed in hardware. 

If a general call address match occurs, the I2CRSR is
transferred to the I2CRCV after the eighth clock, the
RBF flag is set, and on the falling edge of the ninth bit
(ACK bit), the Master Event Interrupt Flag (MI2CIF) is
set.

When the interrupt is serviced, the source for the
interrupt can be checked by reading the contents of the
I2CRCV to determine if the address was device-specific,
or a general call address.

As a Master device, six operations are supported.

• Assert a Start condition on SDA and SCL.

• Assert a Restart condition on SDA and SCL.

• Write to the I2CTRN register initiating 

transmission of data/address.

• Generate a Stop condition on SDA and SCL.

• Configure the I

2

C port to receive data.

• Generate an ACK condition at the end of a 

received byte of data.

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 data direction bit. In
this case, the data direction bit (R_W) is logic ‘0’. Serial
data is transmitted 8 bits at a time. After each byte is
transmitted, an ACK bit is received. Start and Stop con-
ditions 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 data direction bit. In this case, the data
direction bit (R_W) is 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
ACK bit is transmitted. Start and Stop conditions
indicate the beginning and end of transmission.

17.12.1

I

2

C MASTER TRANSMISSION

Transmission of a data byte, a 7-bit address, or the sec-
ond half of a 10-bit address is accomplished by simply
writing a value to I2CTRN register. The user should
only write to I2CTRN when the module is in a WAIT
state. This action will set the buffer full flag (TBF) and
allow the Baud Rate Generator to begin counting and
start the next transmission. Each bit of address/data
will be shifted out onto the SDA pin after the falling
edge of SCL is asserted. The Transmit Status Flag,
TRSTAT (I2CSTAT<14>), indicates that a master
transmit is in progress.

17.12.2

I

2

C MASTER RECEPTION

Master mode reception is enabled by programming the
Receive Enable (RCEN) bit (I2CCON<3>). The I

2

C

module must be idle before the RCEN bit is set, other-
wise the RCEN bit will be disregarded. The Baud Rate
Generator begins counting, and on each rollover, the
state of the SCL pin toggles, and data is shifted in to the
I2CRSR on the rising edge of each clock. 

17.12.3

BAUD RATE GENERATOR 

In I

2

C Master mode, the reload value for the BRG is

located in the I2CBRG register. When the BRG is
loaded with this value, the BRG counts down to ‘0’ and
stops until another reload has taken place. If clock arbi-
tration is taking place, for instance, the BRG is reloaded
when the SCL pin is sampled high.