18 UNIVERSAL SERIAL INTERFACE (USI)
18-36
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
D0
ISIF: Operation Completion Flag Bit
Indicates whether the triggered operation has completed or not.
1 (R):
Completed
0 (R):
Not completed (default)
1 (W):
Reset to 0
0 (W):
Ignored
ISIF is set to 1 when the operation that is specified and triggered using the USI_ISTG register has com-
pleted. At the same time an operation completion interrupt request is sent to the ITC if ISIE/USI_ISIE
register is 1. ISIF is reset by writing 1.
Precautions
18.9
Interface mode setting
Be sure to perform software reset (USIMOD[2:0]/USI_GCFG register = 0x0) and set the interface mode (USI-
MOD[2:0]/USI_GCFG register = 0x1 to 0x5) before changing other USIL configurations.
Receiving control byte in I
2
C slave mode
The external I
2
C master device sends a control byte to the I
2
C slave device when an ACK has been received af-
ter sending a slave address. The subsequent operations of the slave device are determined by the control byte.
SDA line
1: Write (by master)
0: Read (by master)
11: Reserved
10: 32-bit address
01: 16-bit address
00: 8-bit address
Start condition
D7
D6
D5
D4
D3
D2
D1
D0
STA
Reserved
Addr size R/W
ACK
R/W
ACK
ACK
Slave address
Access address
Control byte
9.1 Control Byte Sent from I
Figure 18.
2
C Master
I
2
C master write (data receiving from master)
SDA line
Start condition
Write
16-bit address
and data write
STA
Stop condition
Access address
STP
ACK
ACK
ACK
Slv_Addr
Addr[15:8]
ACK
Addr[7:0]
ACK
DA0
ACK
DA1
0x02
Write data
0
9.2 I
Figure 18.
2
C Master Write (Data Receiving from Master)
The control byte specifies the access address size and writing operations. The received data that follow the
control byte should be used as the address and the data to be written according to the access address size.
I
2
C master read (data transmission to master)
SDA line
Start condition
STA
Stop condition
Trigger to wait
for start condition
STP
ACK
0
Write
32-bit address
and data read
ACK
ACK
Slv_Addr
Start condition
STA
ACK
1
Read
Slv_Addr
Addr[31:24]
ACK
Addr[23:16]
ACK
Addr[15:8]
ACK
Addr[7:0]
ACK
DA0
NAK
DA1
0x05
Access address
Read data
9.3 I
Figure 18.
2
C Master Read (Data Transmission to Master)
The master sends the access address following the control byte. Perform data reception for the control byte
and address data to determine the address from which transmit data is read. After sending an ACK for Addr
0, set ISTGMOD[2:0]/USIL_ISTG register to 0x0 and ISTG/USIL_ISTG register to 1 to wait for a start
condition that will be sent from the master for reading data (for the slave to sent the read data).