PIC16F7X7
10.4.8
I2C MASTER MODE START
CONDITION TIMING
10.4.8.1
WCOL Status Flag
If the user writes the SSPBUF when a Start sequence
is in progress, the WCOL is set and the contents of the
buffer are unchanged (the write doesn’t occur).
To initiate a Start condition, the user sets the Start
Condition Enable bit, SEN (SSPCON2<0>). If the SDA
and SCL pins are sampled high, the Baud Rate
Generator is reloaded with the contents of
SSPADD<6:0> and starts its count. If SCL and SDA are
both sampled high when the Baud Rate Generator
times out (TBRG), the SDA pin is driven low. The action
of the SDA being driven low while SCL is high is the
Start condition and causes the S bit (SSPSTAT<3>) to
be set. Following this, the Baud Rate Generator is
reloaded with the contents of SSPADD<6:0> and
resumes its count. When the Baud Rate Generator
times out (TBRG), the SEN bit (SSPCON2<0>) will be
automatically cleared by hardware, the Baud Rate
Generator is suspended, leaving the SDA line held low
and the Start condition is complete.
Note:
Because queueing of events is not
allowed, writing to the lower 5 bits of
SSPCON2 is disabled until the Start
condition is complete.
Note:
If at the beginning of the Start condition,
the SDA and SCL pins are already sam-
pled low, or if during the Start condition, the
SCL line is sampled low before the SDA
line is driven low, a bus collision occurs,
the Bus Collision Interrupt Flag, BCLIF, is
set, the Start condition is aborted and the
I2C module is reset into its Idle state.
FIGURE 10-19:
FIRST START BIT TIMING
Set S bit (SSPSTAT<3>)
At completion of Start bit,
Write to SEN bit occurs here
SDA = 1,
SCL = 1
hardware clears SEN bit
and sets SSPIF bit
TBRG
TBRG
Write to SSPBUF occurs here
2nd bit
1st bit
SDA
TBRG
SCL
TBRG
S
2004 Microchip Technology Inc.
DS30498C-page 121
MICROCHIP [ MICROCHIP ]
