AT90USB646 datasheet(228/434 Pages) ATMEL

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7593A–AVR–02/06

AT90USB64/128

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.

20.6.6

TWI (Slave) Address Mask Register – TWAMR

• 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. Figure 20-10 shows the address match logic in

detail.

Figure 20-10. TWI Address Match Logic, Block Diagram

• Bit 0 – Res: Reserved Bit

This bit is reserved and will always read as zero.

20.7 Using the TWI

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

765

4321

TWAM[6:0]

–

TWAMR

Read/Write

R/W

Initial Value

000

0000

Address

Match

Address Bit Comparator 0

Address Bit Comparator 6..1

TWAR0

TWAMR0

Address

Bit 0

AT90USB646 Datasheet(PDF) 228 Page - ATMEL Corporation

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