PIC18FXX20
I2C MASTER MODE REPEATED
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).
17.4.9
START CONDITION TIMING
A Repeated START condition occurs when the RSEN
bit (SSPCON2<1>) is programmed high and the I2C
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<5:0> and begins counting. The
SDA pin is released (brought high) for one baud rate
generator count (TBRG). When the baud rate generator
times out, if SDA is sampled high, the SCL pin will be
de-asserted (brought high). When SCL is sampled
high, the baud rate generator is reloaded with the con-
tents of SSPADD<6:0> and begins counting. SDA and
SCL must be sampled high for one TBRG. This action is
then followed by assertion of the SDA pin (SDA = 0) for
17.4.9.1
WCOL Status Flag
If the user writes the SSPBUF when a Repeated
START sequence is in progress, the WCOL is set and
the contents of the buffer are unchanged (the write
doesn’t occur).
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.
one TBRG 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.
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
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".
FIGURE 17-20:
REPEAT START CONDITION WAVEFORM
Set S (SSPSTAT<3>)
Write to SSPCON2
occurs here.
SDA = 1,
SCL = 1
At completion of START bit,
hardware clears RSEN bit
and sets SSPIF
SDA = 1,
SCL (no change).
TBRG
TBRG
TBRG
1st bit
SDA
Write to SSPBUF occurs here
TBRG
Falling edge of ninth clock
End of Xmit
SCL
TBRG
Sr = Repeated START
DS39609A-page 186
Advance Information
2003 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
