AT90USB647-MU Atmel, AT90USB647-MU Datasheet - Page 218
AT90USB647-MU
Manufacturer Part Number
AT90USB647-MU
Description
MCU, 8BIT, 64K FLASH, USB, 64QFN
Manufacturer
Atmel
Specifications of AT90USB647-MU
Controller Family/series
AT90
No. Of I/o's
48
Eeprom Memory Size
2KB
Ram Memory Size
4KB
Cpu Speed
16MHz
No. Of
RoHS Compliant
Core Size
8bit
Program Memory Size
64KB
Oscillator Type
External, Internal
Package
64QFN EP
Device Core
AVR
Family Name
AT90
Maximum Speed
20 MHz
Ram Size
4 KB
Operating Supply Voltage
3.3|5 V
Data Bus Width
8 Bit
Program Memory Type
Flash
Number Of Programmable I/os
48
Interface Type
SPI/TWI/USART/USB
On-chip Adc
8-chx10-bit
Operating Temperature
-40 to 85 °C
Number Of Timers
4
Lead Free Status / Rohs Status
Details
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depicted below, START and STOP conditions are signalled by changing the level of the SDA
line when the SCL line is high.
Figure 20-3. START, REPEATED START and STOP conditions
SDA
SCL
START
STOP
START
REPEATED START
STOP
20.3.3
Address Packet Format
All address packets transmitted on the TWI bus are 9 bits long, consisting of 7 address bits, one
READ/WRITE control bit and an acknowledge bit. If the READ/WRITE bit is set, a read opera-
tion is to be performed, otherwise a write operation should be performed. When a Slave
recognizes that it is being addressed, it should acknowledge by pulling SDA low in the ninth SCL
(ACK) cycle. If the addressed Slave is busy, or for some other reason can not service the Mas-
ter’s request, the SDA line should be left high in the ACK clock cycle. The Master can then
transmit a STOP condition, or a REPEATED START condition to initiate a new transmission. An
address packet consisting of a slave address and a READ or a WRITE bit is called SLA+R or
SLA+W, respectively.
The MSB of the address byte is transmitted first. Slave addresses can freely be allocated by the
designer, but the address 0000 000 is reserved for a general call.
When a general call is issued, all slaves should respond by pulling the SDA line low in the ACK
cycle. A general call is used when a Master wishes to transmit the same message to several
slaves in the system. When the general call address followed by a Write bit is transmitted on the
bus, all slaves set up to acknowledge the general call will pull the SDA line low in the ack cycle.
The following data packets will then be received by all the slaves that acknowledged the general
call. Note that transmitting the general call address followed by a Read bit is meaningless, as
this would cause contention if several slaves started transmitting different data.
All addresses of the format 1111 xxx should be reserved for future purposes.
Figure 20-4. Address Packet Format
Addr MSB
Addr LSB
R/W
ACK
SDA
SCL
1
2
7
8
9
START
AT90USB64/128
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7593K–AVR–11/09
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