12C508 datasheet(31/113 Pages) MICROCHIP

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DS40139E-page 31

PIC12C5XX

7.0.2

SERIAL CLOCK

This SCL input is used to synchronize the data transfer

from and to the device.

7.1

BUS CHARACTERISTICS

The following bus protocol is to be used with the

EEPROM data memory.

• Data transfer may be initiated only when the bus

is not busy.

During data transfer, the data line must remain stable

whenever the clock line is HIGH. Changes in the data

line while the clock line is HIGH will be interpreted as a

START or STOP condition.

Accordingly, the following bus conditions have been

defined (Figure 7-3).

7.1.1

BUS NOT BUSY (A)

Both data and clock lines remain HIGH.

7.1.2

START DATA TRANSFER (B)

A HIGH to LOW transition of the SDA line while the

clock (SCL) is HIGH determines a START condition. All

commands must be preceded by a START condition.

7.1.3

STOP DATA TRANSFER (C)

A LOW to HIGH transition of the SDA line while the

clock (SCL) is HIGH determines a STOP condition. All

operations must be ended with a STOP condition.

7.1.4

DATA VALID (D)

The state of the data line represents valid data when,

after a START condition, the data line is stable for the

duration of the HIGH period of the clock signal.

The data on the line must be changed during the LOW

period of the clock signal. There is one bit of data per

clock pulse.

Each data transfer is initiated with a START condition

and terminated with a STOP condition. The number of

the data bytes transferred between the START and

STOP conditions is determined by the master device

and is theoretically unlimited.

7.1.5

ACKNOWLEDGE

Each receiving device, when addressed, is obliged to

generate an acknowledge after the reception of each

byte. The master device must generate an extra clock

pulse which is associated with this acknowledge bit.

The device that acknowledges has to pull down the

SDA line during the acknowledge clock pulse in such a

way that the SDA line is stable LOW during the HIGH

period of the acknowledge related clock pulse.

course, setup and hold times must be taken into

account. A master must signal an end of data to the

slave by not generating an acknowledge bit on the last

byte that has been clocked out of the slave. In this case,

the slave must leave the data line HIGH to enable the

master to generate the STOP condition (Figure 7-4).

Note:

Acknowledge bits are not generated if an

internal programming cycle is in progress.

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