AT91SAM7S128 Datasheet, PDF (264/495 Pages) ATMEL Corporation – THUMB BASED MICROCONTROLLERS

28.6.5 TWI Status Register
Register Name:
TWI_SR
Access Type:
Read-only
31
30
29
28
27
26
25
24
–
–
–
–
–
–
–
–
23
22
21
20
19
18
17
16
–
–
–
–
–
–
–
–
15
14
13
12
11
10
–
–
–
–
–
–
9
8
–
NACK
7
6
5
4
3
2
1
0
UNRE
OVRE
–
–
–
TXRDY
RXRDY
TXCOMP
• TXCOMP: Transmission Completed
0 = In master, during the length of the current frame. In slave, from START received to STOP received.
1 = When both holding and shift registers are empty and STOP condition has been sent (in Master) or when MSEN is set
(enable TWI).
• RXRDY: Receive Holding Register Ready
0 = No character has been received since the last TWI_RHR read operation.
1 = A byte has been received in the TWI_RHR since the last read.
• TXRDY: Transmit Holding Register Ready
0 = The transmit holding register has not been transferred into shift register. Set to 0 when writing into TWI_THR register.
1 = As soon as data byte is transferred from TWI_THR to internal shifter or if a NACK error is detected, TXRDY is set at the
same time as TXCOMP and NACK. TXRDY is also set when MSEN is set (enable TWI).
• OVRE: Overrun Error
0 = TWI_RHR has not been loaded while RXRDY was set
1 = TWI_RHR has been loaded while RXRDY was set. Reset by read in TWI_SR when TXCOMP is set.
• UNRE: Underrun Error
0 = No underrun error
1 = No valid data in TWI_THR (TXRDY set) while trying to load the data shifter. This action automatically generated a
STOP bit in Master Mode. Reset by read in TWI_SR when TXCOMP is set.
• NACK: Not Acknowledged
0 = Each data byte has been correctly received by the far-end side TWI slave component.
1 = A data byte has not been acknowledged by the slave component. Set at the same time as TXCOMP. Reset after read.
264 AT91SAM7S128 Preliminary
6116A–ATARM–15-Apr-05