atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 253

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

21.6.6
21.7
7766A–AVR–03/08
Using the TWI
TWI (Slave) Address Mask Register – TWAMR
The LSB of TWAR is used to enable recognition of the general call address (0x00). There is an
associated address comparator that looks for the slave address (or general call address if
enabled) in the received serial address. If a match is found, an interrupt request is generated.
• Bits 7..1 – TWA: TWI (Slave) Address Register
These seven bits constitute the slave address of the TWI unit.
• Bit 0 – TWGCE: TWI General Call Recognition Enable Bit
If set, this bit enables the recognition of a General Call given over the 2-wire Serial Bus.
• Bits 7..1 – TWAM: TWI Address Mask
The TWAMR can be loaded with a 7-bit Slave Address mask. Each of the bits in TWAMR can
mask (disable) the corresponding address bit in the TWI Address Register (TWAR). If the mask
bit is set to one then the address match logic ignores the compare between the incoming
address bit and the corresponding bit in TWAR.
detail.
Figure 21-10. TWI Address Match Logic, Block Diagram
• Bit 0 – Res: Reserved Bit
This bit is reserved and will always read as zero.
The AVR TWI is byte-oriented and interrupt based. Interrupts are issued after all bus events, like
reception of a byte or transmission of a START condition. Because the TWI is interrupt-based,
the application software is free to carry on other operations during a TWI byte transfer. Note that
the TWI Interrupt Enable (TWIE) bit in TWCR together with the Global Interrupt Enable bit in
SREG allow the application to decide whether or not assertion of the TWINT Flag should gener-
ate an interrupt request. If the TWIE bit is cleared, the application must poll the TWINT Flag in
order to detect actions on the TWI bus.
When the TWINT Flag is asserted, the TWI has finished an operation and awaits application
response. In this case, the TWI Status Register (TWSR) contains a value indicating the current
Bit
Read/Write
Initial Value
TWAMR0
Address
TWAR0
Bit 0
R/W
7
0
R/W
6
0
Address Bit Comparator 6..1
R/W
5
0
Address Bit Comparator 0
TWAM[6:0]
R/W
4
0
R/W
Figure 21-10
3
0
R/W
2
0
shows the address match logic in
R/W
1
0
ATmega32U4
R
0
0
–
Address
TWAMR
Match
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