PIC16F87X
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9.2.11 I C MASTER MODE TRANSMISSION
9.2.11.3 ACKSTAT STATUS FLAG
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 gener-
ator 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 fall-
ing 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).
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.
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.
1999 Microchip Technology Inc.
DS30292B-page 81
ETC [ ETC ]
