PIC17C7XX Datasheet, PDF (152/328 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM Microcontrollers with 10-bit A/D

PIC17C7XX
15.2.9 I²C MASTER MODE START CONDITION
TIMING
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 genera-
tor is re-loaded 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 (T_BRG),
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. Follow-
ing 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 (T_BRG) 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:
If at the beginning of START condition the
SDA and SCL pins are already sampled
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.
15.2.9.1 WCOL STATUS FLAG
If the user writes the SSPBUF when an START
sequence is in progress, then 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 to the lower 5 bits of
SSPCON2 is disabled until the START
condition is complete.
FIGURE 15-23: FIRST START BIT TIMING
Write to SEN bit occurs here.
SDA = 1,
SCL = 1
T_BRG
Set S bit (SSPSTAT<3>)
At completion of start bit,
Hardware clears SEN bit
and sets SSPIF bit
T_BRG
Write to SSPBUF occurs here
SDA
1st Bit
T_BRG
2nd Bit
SCL
T_BRG
S
DS30289A-page 152
© 1998 Microchip Technology Inc.