PIC17C752 datasheet(149/320 Pages) MICROCHIP

149 / 320 page

Preliminary

DS30264A-page 149

PIC17C75X

15.2.9

I2C MASTER MODE TRANSMISSION

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

either half of a 10-bit address is accomplished by sim-

ply writing 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 trans-

mission. 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 roll over 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 SSPCON2 register

bit6 on the falling edge of the ninth clock. If the master

receives an acknowledge, the acknowledge status bit

(AKSTAT) 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 15-29)

15.2.9.1

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.

15.2.9.2

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.

15.2.9.3

AKSTAT STATUS FLAG

In transmit mode, the AKSTAT bit (SSPCON2<6>) is

cleared when the slave has sent an acknowledge

(ACK = 0), and

is set when the slave does not

acknowledge (ACK = 1). A slave sends an acknowl-

edge when it has recognized its address (including a

general call), or when the slave has properly received

its data.

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