Operational modes, Twi bus control, Twi commands – Rainbow Electronics AT83C24NDS User Manual

Page 6: Frame structure, At83c24

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4234F–SCR–10/05

AT83C24

Operational Modes

TWI Bus Control

The Atmel Two-wire Interface (TWI) interconnects components on a unique two-wire bus, made
up of one clock line and one data line with speeds of up to 400 Kbits per second, based on a
byte-oriented transfer format.

The TWI-bus interface can be used:

–

To configure the AT83C24

–

To select the operating mode of the card: 1.8V, 3V or 5V

–

To configure the automatic activation sequence

–

To start or stop sessions (activation and de-activation sequences)

–

To initiate a warm reset

–

To control the clock to the card in active mode

–

To control the clock to the card in stand-by mode (stop LOW, stop HIGH or running)

–

To enter or leave the card stand-by or power-down modes

–

To select the interface (connection to the host I/O / C4/ C8)

–

To request the status (card present or not, over-current and out of range supply
voltage occurrence)

–

To drive and monitor the card contacts by software

–

To accurately measure the ATR delay when automatic activation is used

TWI Commands

Frame Structure

The structure of the TWI bus data frames is made of one or a series of write and read com-
mands completed by STOP.

Write commands to the AT83C24 have the structure:

ADDRESS BYTE + COMMAND BYTE + DATA BYTE(S)

Read commands to the AT83C24 have the structure:

ADDRESS BYTE + DATA BYTE(S)

The ADDRESS BYTE is sampled on A2/CK, A1/RST, A0/3V after each reset (hard/soft/general
call) but A2/CK, A1/RST, A0/3V can be used for transparent mode after the reset.

Figure 1. Data transfer on TWI bus

SDA

SCL

start condition

stop condition

acknowledgement
from slave

Adresse byte

command
and/or data

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