PIC16F87X datasheet(82/218 Pages) MICROCHIP

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PIC16F87X

DS30292D-page 82

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9.2.11

I2C MASTER MODE

TRANSMISSION

Transmission of a data byte, a 7-bit address, or either

half of a 10-bit address, is accomplished by simply writ-

ing a value to SSPBUF register. This action will set the

Buffer Full flag (BF) 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 (see data hold

time spec). SCL is held low for one baud rate generator

rollover count (TBRG). Data should be valid before SCL

is released high (see data setup time spec). When the

SCL pin is released high, it is held that way for TBRG.

The data on the SDA pin must remain stable for that

duration and some hold time after the next falling edge

of SCL. After the eighth bit is shifted out (the falling

edge of the eighth clock), the BF flag is cleared and the

master releases SDA allowing the slave device being

addressed to respond with an ACK bit during the ninth

bit time, if an address match occurs or if data was

received properly. The status of ACK is read into the

ACKDT on the falling edge of the ninth clock. If the

master receives an Acknowledge, the Acknowledge

Status bit (ACKSTAT) is cleared. If not, the bit is set.

After the ninth clock, the SSPIF is set and the master

clock (baud rate generator) is suspended until the next

data byte is loaded into the SSPBUF, leaving SCL low

and SDA unchanged (Figure 9-14).

After the write to the SSPBUF, each bit of address will

be shifted out on the falling edge of SCL, until all seven

address bits and the R/W bit are completed. On the fall-

ing edge of the eighth clock, the master will de-assert

the SDA pin, allowing the slave to respond with an

Acknowledge. On the falling edge of the ninth clock, the

master will sample the SDA pin to see if the address

was recognized by a slave. The status of the ACK bit is

loaded into the ACKSTAT status bit (SSPCON2<6>).

Following the falling edge of the ninth clock transmis-

sion of the address, the SSPIF is set, the BF flag is

cleared, and the baud rate generator is turned off until

another write to the SSPBUF takes place, holding SCL

low and allowing SDA to float.

9.2.11.1

BF Status Flag

In Transmit mode, the BF bit (SSPSTAT<0>) is set

when the CPU writes to SSPBUF and is cleared when

all 8 bits are shifted out.

9.2.11.2

WCOL Status Flag

If the user writes the SSPBUF when a transmit is

already in progress (i.e., SSPSR is still shifting out a

data byte), then WCOL is set and the contents of the

buffer are unchanged (the write doesn’t occur).

WCOL must be cleared in software.

9.2.11.3

ACKSTAT Status Flag

In Transmit mode, the ACKSTAT bit (SSPCON2<6>) is

cleared when the slave has sent an Acknowledge

(ACK = 0), and is set when the slave does not Acknowl-

edge (ACK = 1). A slave sends an Acknowledge when

it has recognized its address (including a general call),

or when the slave has properly received its data.

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