PIC17C75X
2
15.2.9 I C MASTER MODE TRANSMISSION
15.2.9.1 BF STATUS FLAG
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
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).
for one baud rate generator roll over count (T
).
BRG
Data should be valid before SCL is released high (see
Data setup time spec). When the SCL pin is released
WCOL must be cleared in software.
15.2.9.3 AKSTAT STATUS FLAG
high, it is held that way for T
, the data on the SDA
BRG
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)
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.
1997 Microchip Technology Inc.
Preliminary
DS30264A-page 149
MICROCHIP [ MICROCHIP ]
