PIC18F2455_07 Datasheet, PDF (232/430 Pages) Microchip Technology – 28/40/44-Pin, High Performance, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2455/2550/4455/4550
19.4.12 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 (TBRG)
and the SCL pin is deasserted (pulled high). When the
SCL pin is sampled high (clock arbitration), the Baud
Rate Generator counts for TBRG. 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 an inactive state
(Figure 19-25).
19.4.12.1 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).
19.4.13 STOP CONDITION TIMING
A Stop bit is asserted on the SDA pin at the end of a
receive/transmit by setting the Stop 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 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
deasserted. 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 19-26).
19.4.13.1 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 19-25: ACKNOWLEDGE SEQUENCE WAVEFORM
Acknowledge sequence starts here,
write to SSPCON2
ACKEN = 1, ACKDT = 0
TBRG
TBRG
ACKEN automatically cleared
SDA
D0
ACK
SCL
8
9
SSPIF
Set SSPIF at the
end of receive
Cleared in
software
Note: TBRG = one Baud Rate Generator period.
Cleared in
software
Set SSPIF at the end
of Acknowledge sequence
FIGURE 19-26: STOP CONDITION RECEIVE OR TRANSMIT MODE
Write to SSPCON2,
set PEN
Falling edge of
ninth clock
SCL
TBRG
SCL = 1 for TBRG, followed by SDA = 1 for TBRG
after SDA sampled high. P bit (SSPSTAT<4>) is set.
PEN bit (SSPCON2<2>) is cleared by
hardware and the SSPIF bit is set
SDA
ACK
TBRG
P
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.
DS39632D-page 230
Preliminary
© 2007 Microchip Technology Inc.