PIC18FXX20
17.4.12 ACKNOWLEDGE SEQUENCE
17.4.13 STOP CONDITION TIMING
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
An Acknowledge sequence is enabled by setting the
a
Acknowledge
sequence
enable
bit,
ACKEN
receive/transmit, the SCL line is held low after the fall-
ing 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 TBRG
(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
TBRG later, the PEN bit is cleared and the SSPIF bit is
set (Figure 17-24).
(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 (TBRG) 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 TBRG. 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 17-23).
17.4.13.1 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).
17.4.12.1 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).
FIGURE 17-23:
ACKNOWLEDGE SEQUENCE WAVEFORM
Acknowledge sequence starts here,
Write to SSPCON2
ACKEN automatically cleared
ACKEN = 1, ACKDT = 0
TBRG
ACK
TBRG
SDA
SCL
D0
8
9
SSPIF
Cleared in
Set SSPIF at the end
of receive
Cleared in
software
software
Set SSPIF at the end
of Acknowledge sequence
Note: TBRG = one baud rate generator period.
FIGURE 17-24:
STOP CONDITION RECEIVE OR TRANSMIT MODE
SCL = 1for TBRG, followed by SDA = 1for TBRG
Write to SSPCON2
Set PEN
after SDA sampled high. P bit (SSPSTAT<4>) is set.
PEN bit (SSPCON2<2>) is cleared by
hardware and the SSPIF bit is set
Falling edge of
9th clock
TBRG
SCL
SDA
ACK
P
TBRG
TBRG
TBRG
SCL brought high after TBRG
SDA asserted low before rising edge of clock
to setup STOP condition
Note: TBRG = one baud rate generator period.
DS39609A-page 190
Advance Information
2003 Microchip Technology Inc.
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