18 UNIVERSAL SERIAL INTERFACE (USI)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
18-35
USI I
2
C Slave Mode Interrupt Flag Register (USI_ISIF)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
USI I
2
C Slave
Mode Interrupt
Flag Register
(USI_ISIF)
0x300472
(8 bits)
D7–6 –
reserved
–
–
–
0 when being read.
D5
ISBSY
I
2
C slave busy flag
1 Busy
0 Standby
0
R
D4–2 ISSTA[2:0] I
2
C slave status
ISSTA[2:0]
Status
0x0
R
0x7
0x6
0x5
0x4
0x3
0x2
0x1
0x0
reserved
NAK received
ACK received
ACK/NAK sent
End of Rx data
End of Tx data
Stop detected
Start detected
D1
ISEIF
Overrun error flag
1 Error
0 Normal
0
R/W Reset by writing 1.
D0
ISIF
Operation completion flag
1 Completed 0 Not completed
0
R/W
Note: This register is effective only in I
2
C slave mode. Configure USI to I
2
C slave mode before this reg-
ister can be used.
D[7:6]
Reserved
D5
ISBSY: I
2
C Slave Busy Flag Bit
Indicates the I
2
C slave operation status.
1 (R):
Busy
0 (R):
Standby (default)
Writing 1 to ISTG/USI_ISTG register (starting an I
2
C slave operation) sets ISBSY to 1 indicating that
the I
2
C controller is busy (operating). When the specified operation has finished, ISBSY is reset to 0.
D[4:2]
ISSTA[2:0]: I
2
C Slave Status Bits
Indicates the I
2
C slave status.
8.6 I
Table 18.
2
C Slave Status Bits
ISSTA[2:0]
Status
0x7
Reserved
0x6
NAK has been received.
0x5
ACK has been received.
0x4
ACK or NAK has been sent.
0x3
End of receive data.
0x2
End of transmit data.
0x1
Stop condition has been detected.
0x0
Start condition has been detected.
(Default: 0x0)
When an operation completion interrupt occurs, read ISSTA[2:0] to check the operation that has been
finished. ISSTA[2:0] is automatically reset to 0x0 by writing 1 to ISIF.
D1
ISEIF: Overrun Error Flag Bit
Indicates whether an overrun error has occurred or not.
1 (R):
Error occurred
0 (R):
No error (default)
1 (W):
Reset to 0
0 (W):
Ignored
ISEIF is set to 1 when an overrun error occurs. At the same time a receive error interrupt request is sent
to the ITC if ISEIE/USI_ISIE register is 1. An overrun error occurs when a transmit or receive trigger is
issued after two-byte data has been received (the first byte data exists in the receive data buffer and the
second byte data exists in the shift register) without the receive data buffer being read.
ISEIF is reset by writing 1.
To reset an overrun error, clear ISEIF by writing 1, and then read the receive data buffer (USI_RD regis-
ter) twice.