AT89C51ID2-RDTIM datasheet(84/159 Pages) ATMEL

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AT89C51ID2

4289A–8051–09/03

W: Write bit (low level at SDA)

A: Acknowledge bit (low level at SDA)

A: Not acknowledge bit (high level at SDA)

Data: 8-bit data byte

P : STOP condition

In Figure 33 to Figure 36, circles are used to indicate when the serial interrupt flag is set.

The numbers in the circles show the status code held in SSCS. At these points, a ser-

vice routine must be executed to continue or complete the serial transfer. These service

routines are not critical since the serial transfer is suspended until the serial interrupt

flag is cleared by software.

When the serial interrupt routine is entered, the status code in SSCS is used to branch

to the appropriate service routine. For each status code, the required software action

and details of the following serial transfer are given in Table to Table 69.

Master Transmitter Mode

In the master transmitter mode, a number of data bytes are transmitted to a slave

receiver (Figure 33). Before the master transmitter mode can be entered, SSCON must

be initialised as follows:

CR0, CR1 and CR2 define the internal serial bit rate if external bit rate generator is not

used. SSIE must be set to enable TWI. STA, STO and SI must be cleared.

The master transmitter mode may now be entered by setting the STA bit. The 2-wire

logic will now test the 2-wire bus and generate a START condition as soon as the bus

becomes free. When a START condition is transmitted, the serial interrupt flag (SI bit in

SSCON) is set, and the status code in SSCS will be 08h. This status must be used to

vector to an interrupt routine that loads SSDAT with the slave address and the data

direction bit (SLA+W).

When the slave address and the direction bit have been transmitted and an acknowl-

edgement bit has been received, SI is set again and a number of status code in SSCS

are possible. There are 18h, 20h or 38h for the master mode and also 68h, 78h or B0h if

the slave mode was enabled (AA=logic 1). The appropriate action to be taken for each

of these status code is detailed in Table . This scheme is repeated until a STOP condi-

tion is transmitted.

SSIE, CR2, CR1 and CR0 are not affected by the serial transfer and are referred to

Table 7 to Table 11. After a repeated START condition (state 10h) the TWI module may

switch to the master receiver mode by loading SSDAT with SLA+R.

Master Receiver Mode

In the master receiver mode, a number of data bytes are received from a slave transmit-

ter (Figure 34). The transfer is initialized as in the master transmitter mode. When the

START condition has been transmitted, the interrupt routine must load SSDAT with the

7-bit slave address and the data direction bit (SLA+R). The serial interrupt flag SI must

then be cleared before the serial transfer can continue.

Table 61. SSCON Initialization

CR2

SSIE

STA

STO

CR1

CR0

bit rate

AT89C51ID2-RDTIM Datasheet(PDF) 84 Page - ATMEL Corporation

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