Rainbow Electronics ATmega163L - Manual (Page 72)

ATmega163(L)
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ator that looks for the slave address (or generall call address if enabled) in the received serial address. If a match is found,
an interrupt request is generated.
2-wire Serial Interface Modes
The 2-wire Serial Interface can operate in four different modes:
• Master Transmitter
• Master Receiver
• Slave Receiver
• Slave Transmitter
Data transfer in each mode of operation is shown in 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)
A: Acknowledge bit (low level at SDA)
A: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 52 to Figure 55, circles are used to indicate that the 2-wire Serial Interface interrupt flag is set. The numbers in the
circles show the status code held in TWSR. At these points, actions must be taken by the application to continue or com-
plete the 2-wire Serial Bus transfer. The 2-wire Serial Bus transfer is suspended until the 2-wire Serial Interface interrupt
flag is cleared by software.
The 2-wire Serial Interface interrupt flag is not automatically cleared by hardware when executing the interrupt routine.
Software has to clear the flag to continue the 2-wire transfer. Also note that the 2-wire Serial Interface starts execution as
soon as this bit is cleared, so that all access to TWAR, TWDR, and TWSR must have been completed before clearing this
flag.
When the 2-wire Serial Interface interrupt flag is set, the status code in TWSR is used to determine the appropriate soft-
ware action. For each status code, the required software action and details of the following serial transfer are given in Table
32 to Table 36.
Master Transmitter Mode
In the master transmitter mode, a number of data bytes are transmitted to a slave receiver (see Figure 52). Before master
transmitter mode can be entered, the TWCR must be initialized as follows:
TWEN must be set to enable the 2-wire Serial Interface, TWSTA and TWSTO must be cleared.
The master transmitter mode may now be entered by setting the TWSTA bit. The 2-Wire Serial Interface logic will then test
the 2-wire Serial Bus and generate a START condition as soon as the bus becomes free. When a START condition is
transmitted, the 2-wire Serial Interface interrupt flag (TWINT) is set by hardware, and the status code in TWSR will be $08.
TWDR must then be loaded with the slave address and the data direction bit (SLA+W). Clearing the TWINT bit in software
will continue the transfer. The TWINT flag is cleared by writing a logic one to the flag.
When the slave address and the direction bit have been transmitted and an acknowledgement bit has been received,
TWINT is set again and a number of status codes in TWSR are possible. Possible status codes in master mode are $18,
$20, or $38. The appropriate action to be taken for each of these status codes is detailed in Table 32. The data must be
loaded when TWINT is high only. If not, the access will be discarded, and the Write Collision bit - TWWC will be set in the
Table 29. TWCR: Master Transmitter Mode Initialization
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN - TWIE
value 0 X 0 0 0 1 0 X