PIC16F874A-I/PT【PDF 4/234 页】IC MCU FLASH 4K 20MHZ 44-TQFP

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2003 Microchip Technology Inc.

DS39582B-page 99

PIC16F87XA

9.4.8

I2C MASTER MODE START

CONDITION TIMING

To initiate a Start condition, the user sets the Start con-

dition 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 con-

tents 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 hard-

ware, the Baud Rate Generator is suspended, leaving

the SDA line held low and the Start condition is

complete.

9.4.8.1

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).

FIGURE 9-19:

FIRST START BIT TIMING

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.

Note:

Because queueing of events

not

allowed, writing to the lower 5 bits of

SSPCON2 is disabled until the Start

condition is complete.

SDA

SCL

TBRG

1st Bit

2nd Bit

TBRG

SDA = 1,

At completion of Start bit,

SCL = 1

Write to SSPBUF occurs here

TBRG

hardware clears SEN bit

TBRG

Write to SEN bit occurs here

Set S bit (SSPSTAT<3>)

and sets SSPIF bit

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