Microchip Technology MA180025 データシート
PIC18F87J90 FAMILY
DS39933D-page 244
2010 Microchip Technology Inc.
18.4.9
I
2
C MASTER MODE REPEATED
START CONDITION TIMING
A Repeated Start condition occurs when the RSEN bit
(SSPCON2<1>) is programmed high and the I
(SSPCON2<1>) is programmed high and the I
2
C logic
module is in the Idle state. When the RSEN bit is set,
the SCL pin is asserted low. When the SCL pin is
sampled low, the Baud Rate Generator is loaded with
the contents of SSPADD<6:0> and begins counting.
The SDA pin is released (brought high) for one Baud
Rate Generator count (T
the SCL pin is asserted low. When the SCL pin is
sampled low, the Baud Rate Generator is loaded with
the contents of SSPADD<6:0> and begins counting.
The SDA pin is released (brought high) for one Baud
Rate Generator count (T
BRG
). When the Baud Rate
Generator times out, if SDA is sampled high, the SCL
pin will be deasserted (brought high). When SCL is
sampled high, the Baud Rate Generator is reloaded
with the contents of SSPADD<6:0> and begins
counting. SDA and SCL must be sampled high for one
T
pin will be deasserted (brought high). When SCL is
sampled high, the Baud Rate Generator is reloaded
with the contents of SSPADD<6:0> and begins
counting. SDA and SCL must be sampled high for one
T
BRG
. This action is then followed by assertion of the
SDA pin (SDA = 0) for one T
BRG
while SCL is high.
Following this, the RSEN bit (SSPCON2<1>) will be
automatically cleared and the Baud Rate Generator will
not be reloaded, leaving the SDA pin held low. As soon
as a Start condition is detected on the SDA and SCL
pins, the S bit (SSPSTAT<3>) will be set. The SSPIF bit
will not be set until the Baud Rate Generator has timed
out.
automatically cleared and the Baud Rate Generator will
not be reloaded, leaving the SDA pin held low. As soon
as a Start condition is detected on the SDA and SCL
pins, the S bit (SSPSTAT<3>) will be set. The SSPIF bit
will not be set until the Baud Rate Generator has timed
out.
Immediately following the SSPIF bit getting set, the user
may write the SSPBUF with the 7-bit address in 7-bit
mode or the default first address in 10-bit mode. After the
first eight bits are transmitted and an ACK is received,
the user may then transmit an additional eight bits of
address (10-bit mode) or eight bits of data (7-bit mode).
may write the SSPBUF with the 7-bit address in 7-bit
mode or the default first address in 10-bit mode. After the
first eight bits are transmitted and an ACK is received,
the user may then transmit an additional eight bits of
address (10-bit mode) or eight bits of data (7-bit mode).
18.4.9.1
WCOL Status Flag
If the user writes the SSPBUF when a Repeated Start
sequence is in progress, the WCOL flag is set and the
contents of the buffer are unchanged (the write doesn’t
occur).
sequence is in progress, the WCOL flag is set and the
contents of the buffer are unchanged (the write doesn’t
occur).
FIGURE 18-22:
REPEATED START CONDITION WAVEFORM
Note 1: If RSEN is programmed while any other
event is in progress, it will not take effect.
2: A bus collision during the Repeated Start
condition occurs if:
• SDA is sampled low when SCL goes
• SDA is sampled low when SCL goes
from low-to-high.
• SCL goes low before SDA is
asserted low. This may indicate that
another master is attempting to
transmit a data ‘1’.
another master is attempting to
transmit a data ‘1’.
Note:
Because queueing of events is not
allowed, writing of the lower 5 bits of
SSPCON2 is disabled until the Repeated
Start condition is complete.
allowed, writing of the lower 5 bits of
SSPCON2 is disabled until the Repeated
Start condition is complete.
SDA
SCL
Sr = Repeated Start
Write to SSPCON2
Write to SSPBUF occurs here
on falling edge of ninth clock,
end of XMIT
At completion of Start bit,
hardware clears RSEN bit
hardware clears RSEN bit
1st bit
S bit set by hardware
T
BRG
T
BRG
SDA = 1,
SDA = 1,
SCL (no change)
SCL = 1
occurs here:
T
BRG
T
BRG
and sets SSPIF
RSEN bit set by hardware
T
BRG