Datasheet

PIC18F2480/2580/4480/4580
DS39637D-page 224 © 2009 Microchip Technology Inc.
18.4.12 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
Generator then counts for one rollover period (T
BRG)
and the SCL pin is deasserted (pulled high). When the
SCL pin is sampled high (clock arbitration), the Baud
Rate Generator counts for T
BRG; the SCL pin is then
pulled low. Following this, the ACKEN bit is automatically
cleared, the Baud Rate Generator is turned off and the
MSSP module then goes into Idle mode (Figure 18-23).
18.4.12.1 WCOL Status Flag
If the user writes the SSPBUF when an Acknowledge
sequence is in progress, then WCOL is set and the
contents of the buffer are unchanged (the write doesn’t
occur).
18.4.13 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/
transmit, 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 sam-
pled 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 deasserted. 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 18-24).
18.4.13.1 WCOL Status Flag
If the user writes the SSPBUF when a Stop sequence
is in progress, then the WCOL bit is set and the
contents of the buffer are unchanged (the write doesn’t
occur).
FIGURE 18-23: ACKNOWLEDGE SEQUENCE WAVEFORM
FIGURE 18-24: STOP CONDITION RECEIVE OR TRANSMIT MODE
Note: TBRG = one Baud Rate Generator period.
SDA
SCL
Set SSPIF at the
Acknowledge sequence starts here,
write to SSPCON2
ACKEN automatically cleared
Cleared in
TBRG
TBRG
end of receive
8
ACKEN = 1, ACKDT = 0
D0
9
SSPIF
software
Set SSPIF at the end
of Acknowledge sequence
Cleared in
software
ACK
SCL
SDA
SDA asserted low before rising edge of clock
Write to SSPCON2,
set PEN
Falling edge of
SCL = 1 for TBRG, 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 set up Stop condition
ACK
P
T
BRG
PEN bit (SSPCON2<2>) is cleared by
hardware and the SSPIF bit is set