Datasheet

PIC18FXX2
DS39564C-page 158 © 2006 Microchip Technology Inc.
15.4.12 ACKNOWLEDGE SEQUENCE
TIMING
An Acknowledge sequence is enabled by setting the
Acknowledge sequence enable bit, ACKEN
(SSPCON2<4>). When this bit is set, the SCL pin is
pulled low and the contents of the Acknowledge data bit
are presented on the SDA pin. If the user wishes to gen-
erate an Acknowledge, then the ACKDT bit should be
cleared. If not, the user should set the ACKDT bit before
starting an Acknowledge sequence. The baud rate gen-
erator then counts for one rollover period (T
BRG) and the
SCL pin is de-asserted (pulled high). When the SCL pin
is sampled high (clock arbitration), the baud rate gener-
ator counts for T
BRG. The SCL pin is then pulled low. Fol-
lowing this, the ACKEN bit is automatically cleared, the
baud rate generator is turned off and the MSSP module
then goes into IDLE mode (Figure 15-23).
15.4.12.1 WCOL Status Flag
If the user writes the SSPBUF when an Acknowledge
sequence is in progress, then WCOL is set and the con-
tents of the buffer are unchanged (the write doesn’t occur).
15.4.13 STOP CONDITION TIMING
A STOP bit is asserted on the SDA pin at the end of a
receive/transmit by setting the STOP sequence enable
bit, PEN (SSPCON2<2>). At the end of a receive/trans-
mit the SCL line is held low after the falling edge of the
ninth clock. When the PEN bit is set, the master will
assert the SDA line low. When the SDA line is sampled
low, the baud rate generator is reloaded and counts
down to 0. When the baud rate generator times out, the
SCL pin will be brought high, and one T
BRG (baud rate
generator rollover count) later, the SDA pin will be
de-asserted. When the SDA pin is sampled high while
SCL is high, the P bit (SSPSTAT<4>) is set. A T
BRG
later, the PEN bit is cleared and the SSPIF bit is set
(Figure 15-24).
15.4.13.1 WCOL Status Flag
If the user writes the SSPBUF when a STOP sequence
is in progress, then the WCOL bit is set and the con-
tents of the buffer are unchanged (the write doesn’t
occur).
FIGURE 15-23: ACKNOWLEDGE SEQUENCE WAVEFORM
FIGURE 15-24: STOP CONDITION RECEIVE OR TRANSMIT MODE
Note: TBRG = one baud rate generator period.
SDA
SCL
Set SSPIF at the end
Acknowledge sequence starts here,
Write to SSPCON2
ACKEN automatically cleared
Cleared in
TBRG
TBRG
of receive
ACK
8
ACKEN = 1, ACKDT = 0
D0
9
SSPIF
software
Set SSPIF at the end
of Acknowledge sequence
Cleared in
software
SCL
SDA
SDA asserted low before rising edge of clock
Write to SSPCON2
Set PEN
Falling edge of
SCL = 1 for T
BRG, followed by SDA = 1 for TBRG
9th clock
SCL brought high after T
BRG
Note: TBRG = one baud rate generator period.
TBRG
TBRG
after SDA sampled high. P bit (SSPSTAT<4>) is set.
T
BRG
to setup STOP condition.
ACK
P
T
BRG
PEN bit (SSPCON2<2>) is cleared by
hardware and the SSPIF bit is set