Datasheet

ATmega32A
 2018 Microchip Technology Inc. Data Sheet Complete DS40002072A-page 182
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 21-12 to Figure 21-18, circles are used to indicate that the TWINT Flag is set. The numbers in the circles
show the status code held in TWSR, with the prescaler bits masked to zero. At these points, actions must be taken
by the application to continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT Flag is
cleared by software.
When the TWINT Flag is set, the status code in TWSR is used to determine the appropriate software action. For
each status code, the required software action and details of the following serial transfer are given in Table 21-2 to
Table 21-5. Note that the prescaler bits are masked to zero in these tables.
21.7.1 Master Transmitter Mode
In the Master Transmitter mode, a number of data bytes are transmitted to a slave receiver (see Figure 21-11). In
order to enter a Master mode, a START condition must be transmitted. The format of the following address packet
determines whether Master Transmitter or Master Receiver mode is to be entered. If SLA+W is transmitted, MT
mode is entered, if SLA+R is transmitted, MR mode is entered. All the status codes mentioned in this section
assume that the prescaler bits are zero or are masked to zero.
Figure 21-11. Data Transfer in Master Transmitter Mode
A START condition is sent by writing the following value to TWCR:
TWEN must be set to enable the Two-wire Serial Interface, TWSTA must be written to one to transmit a START
condition and TWINT must be written to one to clear the TWINT Flag. The TWI will then test the Two-wire Serial
Bus and generate a START condition as soon as the bus becomes free. After a START condition has been trans-
mitted, the TWINT Flag is set by hardware, and the status code in TWSR will be $08 (See Table 21-2). In order to
enter MT mode, SLA+W must be transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT bit
should be cleared (by writing it to one) to continue the transfer. This is accomplished by writing the following value
to TWCR:
When SLA+W 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 21-2.
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE
Value 1
X10X10 X
TWCR TWINT
TWEA TWSTA TWSTO TWWC TWEN – TWIE
Value 1
X00X10 X
Device 1
MASTER
TRANSMITTER
Device 2
SLAVE
RECEIVER
Device 3
Device n
SDA
SCL
........
R1 R2
V
CC