AT89C5131A-RDTIL datasheet(101/184 Pages) ATMEL

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101

AT89C5131A-L

4338F–USB–08/07

Description

The CPU interfaces to the 2-wire logic via the following four 8-bit special function regis-

ters: the Synchronous Serial Control register (SSCON; Table 86), the Synchronous

Serial Data register (SSDAT; Table 87), the Synchronous Serial Control and Status reg-

ister (SSCS; Table 88) and the Synchronous Serial Address register (SSADR Table 89).

SSCON is used to enable the TWI interface, to program the bit rate (see Table 79), to

enable slave modes, to acknowledge or not a received data, to send a START or a

STOP condition on the 2-wire bus, and to acknowledge a serial interrupt. A hardware

reset disables the TWI module.

SSCS contains a status code which reflects the status of the 2-wire logic and the 2-wire

bus. The three least significant bits are always zero. The five most significant bits con-

tains the status code. There are 26 possible status codes. When SSCS contains F8h,

no relevant state information is available and no serial interrupt is requested. A valid sta-

tus code is available in SSCS one machine cycle after SI is set by hardware and is still

present one machine cycle after SI has been reset by software. to Table 85. give the

status for the master modes and miscellaneous states.

SSDAT contains a byte of serial data to be transmitted or a byte which has just been

received. It is addressable while it is not in process of shifting a byte. This occurs when

2-wire logic is in a defined state and the serial interrupt flag is set. Data in SSDAT

remains stable as long as SI is set. While data is being shifted out, data on the bus is

simultaneously shifted in; SSDAT always contains the last byte present on the bus.

SSADR may be loaded with the 7-bit slave address (7 most significant bits) to which the

TWI module will respond when programmed as a slave transmitter or receiver. The LSB

is used to enable general call address (00h) recognition.

Figure 51 shows how a data transfer is accomplished on the 2-wire bus.

Figure 51. Complete Data Transfer on 2-wire Bus

The four operating modes are:

•

Master Transmitter

•

Master Receiver

•

Slave transmitter

•

Slave receiver

Data transfer in each mode of operation is shown in Table to Table 85 and Figure 52. to

Figure 55.. These figures contain the following abbreviations:

S : START condition

R : Read bit (high level at SDA)

W: Write bit (low level at SDA)

SDA

SCL

start

condition

MSB

ACK

acknowledgement

signal from receiver

acknowledgement

signal from receiver

3-8

ACK

stop

condition

clock line held low

while interrupts are serviced

AT89C5131A-RDTIL 数据表(PDF) 101 Page - ATMEL Corporation

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