AT83SND1CXXX-ROTIL datasheet(159/212 Pages) ATMEL

159 / 212 page

159

4109J–8051–10/06

AT8xC51SND1C

Note:

1. These bit rates are outside of the low speed standard specification limited to 100 kHz but can

be used with high speed TWI components limited to 400 kHz.

19.1.2

Master Transmitter Mode

In the master transmitter mode, a number of data Bytes are transmitted to a slave receiver (see

Figure 19-3). Before the master transmitter mode can be entered, SSCON must be initialized as

follows:

SSCR2:0 define the serial bit rate (see Table 125). SSPE must be set to enable the controller.

SSSTA, SSSTO and SSI must be cleared.

The master transmitter mode may now be entered by setting the SSSTA bit. The TWI logic will

now monitor the TWI bus and generate a START condition as soon as the bus becomes free.

When a START condition is transmitted, the serial interrupt flag (SSI bit in SSCON) is set, and

the status code in SSSTA is 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). The serial interrupt flag

(SSI) must then be cleared before the serial transfer can continue.

When the slave address and the direction bit have been transmitted and an acknowledgment bit

has been received, SSI is set again and a number of status code in SSSTA are possible. There

are 18h, 20h or 38h for the master mode and also 68h, 78h or B0h if the slave mode was

enabled (SSAA = logic 1). The appropriate action to be taken for each of these status code is

detailed in Table 126. This scheme is repeated until a STOP condition is transmitted.

SSPE and SSCR2:0 are not affected by the serial transfer and are not referred to in Table 126.

After a repeated START condition (state 10h) the controller may switch to the master receiver

mode by loading SSDAT with SLA+R.

19.1.3

Master Receiver Mode

In the master receiver mode, a number of data Bytes are received from a slave transmitter (see

Figure 19-4). The transfer is initialized as in the master transmitter mode. When the START con-

dition 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 (SSI) must then be cleared before

the serial transfer can continue.

Table 125. Serial Clock Rates

SSCRx

Bit Frequency (kHz)

FPER Divided By

210

FPER = 6 MHz

FPER = 8 MHz

FPER = 10 MHz

62.5

78.125

128

53.5

71.5

89.3

112

62.5

104.2

(1)

100

125

(1)

12.5

16.5

20.83

480

100

133.3

(1)

166.7

(1)

110

200

(1)

266.7

(1)

333.3

(1)

0.5 <

⋅ < 125(1)

0.67 <

⋅ < 166.7(1) 0.81 < ⋅ < 208.3(1) 96 ⋅ (256 – reload value Timer 1)

SSCR2

SSPE

SSSTA

SSSTO

SSI

SSAA

SSCR1

SSCR0

Bit Rate

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