PIC16F720-ESLASHML datasheet(150/244 Pages) MICROCHIP

150 / 244 page

PIC16F/LF720/721

DS41430A-page 150

 2010 Microchip Technology Inc.

17.2.2

START AND STOP CONDITIONS

During times of no data transfer (Idle time), both the

clock line (SCL) and the data line (SDA) are pulled high

through external pull-up resistors. The Start and Stop

conditions determine the start and stop of data trans-

mission. The Start condition is defined as a high-to-low

transition of the SDA line while SCL is high. The Stop

condition is defined as a low-to-high transition of the

SDA line while SCL is high.

Figure 17-9 shows the Start and Stop conditions. A

master device generates these conditions for starting

and terminating data transfer. Due to the definition of

the Start and Stop conditions, when data is being trans-

mitted, the SDA line can only change state when the

SCL line is low.

FIGURE 17-9:

START AND STOP CONDITIONS

17.2.3

ACKNOWLEDGE

After the valid reception of an address or data byte, the

hardware automatically will generate the Acknowledge

(ACK) pulse and load the SSPBUF register with the

received value currently in the SSPSR register. There

are certain conditions that will cause the SSP module

not to generate this ACK pulse. They include any or all

of the following:

• The Buffer Full bit, BF of the SSPSTAT register,

was set before the transfer was received.

• The SSP Overflow bit, SSPOV of the SSPCON

• The SSP module is being operated in Firmware

Master mode.

In such a case, the SSPSR register value is not loaded

into the SSPBUF, but bit SSPIF of the PIR1 register is

set. Table 17-2 shows the results of when a data

transfer byte is received, given the status of bits BF and

SSPOV. Flag bit BF is cleared by reading the SSPBUF

SDA

SCL

Stop

Condition

Start

Condition

Change of

Data Allowed

Change of

Data Allowed

TABLE 17-2:

DATA TRANSFER RECEIVED BYTE ACTIONS

Status Bits as Data

Transfer is Received

SSPSR

 SSPBUF

Generate ACK

Pulse

Set bit SSPIF

(SSP Interrupt occurs

if enabled)

SSPOV

Yes

Note 1:

Shaded cells show the conditions where the user software did not properly clear the overflow condition.

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