AT90USB647-MU Atmel, AT90USB647-MU Datasheet - Page 225
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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20.6.3
7593K–AVR–11/09
TWI Status Register – TWSR
By writing the TWEA bit to zero, the device can be virtually disconnected from the 2-wire Serial
Bus temporarily. Address recognition can then be resumed by writing the TWEA bit to one
again.
• Bit 5 – TWSTA: TWI START Condition Bit
The application writes the TWSTA bit to one when it desires to become a Master on the 2-wire
Serial Bus. The TWI hardware checks if the bus is available, and generates a START condition
on the bus if it is free. However, if the bus is not free, the TWI waits until a STOP condition is
detected, and then generates a new START condition to claim the bus Master status. TWSTA
must be cleared by software when the START condition has been transmitted.
• Bit 4 – TWSTO: TWI STOP Condition Bit
Writing the TWSTO bit to one in Master mode will generate a STOP condition on the 2-wire
Serial Bus. When the STOP condition is executed on the bus, the TWSTO bit is cleared auto-
matically. In Slave mode, setting the TWSTO bit can be used to recover from an error condition.
This will not generate a STOP condition, but the TWI returns to a well-defined unaddressed
Slave mode and releases the SCL and SDA lines to a high impedance state.
• Bit 3 – TWWC: TWI Write Collision Flag
The TWWC bit is set when attempting to write to the TWI Data Register – TWDR when TWINT is
low. This flag is cleared by writing the TWDR Register when TWINT is high.
• Bit 2 – TWEN: TWI Enable Bit
The TWEN bit enables TWI operation and activates the TWI interface. When TWEN is written to
one, the TWI takes control over the I/O pins connected to the SCL and SDA pins, enabling the
slew-rate limiters and spike filters. If this bit is written to zero, the TWI is switched off and all TWI
transmissions are terminated, regardless of any ongoing operation.
• Bit 1 – Res: Reserved Bit
This bit is a reserved bit and will always read as zero.
• Bit 0 – TWIE: TWI Interrupt Enable
When this bit is written to one, and the I-bit in SREG is set, the TWI interrupt request will be acti-
vated for as long as the TWINT Flag is high.
• Bits 7..3 – TWS: TWI Status
These 5 bits reflect the status of the TWI logic and the 2-wire Serial Bus. The different status
codes are described later in this section. Note that the value read from TWSR contains both the
5-bit status value and the 2-bit prescaler value. The application designer should mask the pres-
Bit
Read/Write
Initial Value
1. The device’s own slave address has been received.
2. A general call has been received, while the TWGCE bit in the TWAR is set.
3. A data byte has been received in Master Receiver or Slave Receiver mode.
TWS7
R
7
1
TWS6
R
6
1
TWS5
R
5
1
TWS4
4
R
1
TWS3
R
3
1
R
2
–
0
TWPS1
R/W
AT90USB64/128
1
0
TWPS0
R/W
0
0
TWSR
225
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