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Sheet目录3841

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PIC18F2X1X/4X1X

DS39636D-page 186

2009 Microchip Technology Inc.

16.4.12

ACKNOWLEDGE SEQUENCE

TIMING

An Acknowledge sequence is enabled by setting the

Acknowledge

Sequence

Enable

bit,

ACKEN

(SSPCON2<4>). When this bit is set, the SCL pin is

pulled low and the contents of the Acknowledge data bit

are presented on the SDA pin. If the user wishes to gen-

erate an Acknowledge, then the ACKDT bit should be

cleared. If not, the user should set the ACKDT bit before

starting an Acknowledge sequence. The Baud Rate

Generator then counts for one rollover period (TBRG)

and the SCL pin is deasserted (pulled high). When the

SCL pin is sampled high (clock arbitration), the Baud

Rate Generator counts for TBRG. The SCL pin is then

pulled low. Following this, the ACKEN bit is automatically

cleared, the Baud Rate Generator is turned off and the

MSSP module then goes into Idle mode (Figure 16-23).

16.4.12.1

WCOL Status Flag

If the user writes the SSPBUF when an Acknowledge

sequence is in progress, then WCOL is set and the

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

occur).

16.4.13

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/

transmit, 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 deasserted. When the SDA pin is sam-

pled high while SCL is high, the P bit (SSPSTAT<4>) is

set. A TBRG later, the PEN bit is cleared and the SSPIF

bit is set (Figure 16-24).

16.4.13.1

WCOL Status Flag

If the user writes the SSPBUF when a Stop sequence

is in progress, then the WCOL bit is set and the

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

occur).

FIGURE 16-23:

ACKNOWLEDGE SEQUENCE WAVEFORM

FIGURE 16-24:

STOP CONDITION RECEIVE OR TRANSMIT MODE

Note: TBRG = one Baud Rate Generator period.

SDA

SCL

SSPIF set at

Acknowledge sequence starts here,

write to SSPCON2

ACKEN automatically cleared

Cleared in

TBRG

the end of receive

ACKEN = 1, ACKDT = 0

SSPIF

software

SSPIF set at the end

of Acknowledge sequence

Cleared in

software

ACK

SCL

SDA

SDA asserted low before rising edge of clock

Write to SSPCON2,

set PEN

Falling edge of

SCL = 1 for TBRG, followed by SDA = 1 for TBRG

9th clock

SCL brought high after TBRG

Note: TBRG = one Baud Rate Generator period.

TBRG

after SDA sampled high. P bit (SSPSTAT<4>) is set.

TBRG

to setup Stop condition

ACK

TBRG

PEN bit (SSPCON2<2>) is cleared by

hardware and the SSPIF bit is set

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