PIC17C752 datasheet(157/320 Pages) MICROCHIP

157 / 320 page

Preliminary

DS30264A-page 157

PIC17C75X

15.2.12 STOP CONDITION TIMING

A stop bit is asserted on the SDA pin at the end of a

receive/transmit by setting the Stop Sequence Enable

bit PEN (SSPCON2<2>). At the end of a receive/trans-

mit 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 sam-

pled 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 de-asserted. When the SDA pin is

sampled high while SCL is high, the PEN bit will be

automatically cleared, and the P bit (SSPSTAT<4>) is

set which in turn will set the SSPIF ﬂag. (Figure 15-34)

Whenever the CPU decides to take control of the bus,

it will ﬁrst determine if the bus is busy by checking the

S and P bits in the SSPSTAT register. If the bus is

busy, then the CPU can be interrupted (notiﬁed) when

a Stop bit is detected (i.e. bus is free).

15.2.12.1 WCOL STATUS FLAG

If the user writes the SSPBUF when a STOP

sequence is in progress, then WCOL is set and the

contents of the buffer are unchanged (the write doesn’t

occur).

FIGURE 15-34: STOP CONDITION RECEIVE OR TRANSMIT MODE

SCL

SDA

SDA asserted low before rising edge of clock

Write to SSPCON2

Set PEN

Falling edge of

SCL = 1 for T

BRG, followed by SDA = 1 for TBRG

9th clock

SCL brought high after T

BRG

Note: T

BRG = one baud rate generator period.

BRG

after SDA sampled high, PEN bit (SSPCON2<2>) is

BRG

to setup stop condition.

automatically cleared. P bit (SSPSTAT<4>) is set

ACK

BRG

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