18 UNIVERSAL SERIAL INTERFACE (USI)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
18-11
0x0
Address
0x6
0x2
0x2
Transfer data 1
A6
A5
D7
D6
D5
D4
D3
D2
D1
D0
A4
A3
A2
A1
A0 R/W = 0
ACK
USI_CK pin (output)
USI_CK pin (input)
USI_DI pin (output)
USI_DI pin (input)
IMTGMOD[2:0]
IMTG (write)
IMBSY
IMSTA[2:0]
TD[7:0]
IMIF
Start interrupt
End of transmission
interrupt
End of transmission
interrupt
Receive
ACK interrupt
0x0
*
*
*
*
0x2
0x5
0x2
(1) Start condition
→
Data transmission
0x6
0x6
0x2
0x1
Transfer data n
D7
D6
D5
D4
D3
D2
D1
D0
ACK
ACK
USI_CK pin (output)
USI_CK pin (input)
USI_DI pin (output)
USI_DI pin (input)
IMTGMOD[2:0]
IMTG (write)
IMBSY
IMSTA[2:0]
TD[7:0]
IMIF
Stop interrupt
End of transmission
interrupt
Receive
ACK interrupt
Receive
ACK interrupt
*
*
*
*
*
0x2
0x1
0x5
0x5
(2) Data transmission
→
Stop condition
*
When IMIF is cleared via software, IMSTA[2:0] is also cleared to 0x0.
5.3.2 I
Figure 18.
2
C Master Data Transmission Timing Chart
(1) Generating start condition
I
2
C data transfer starts when the I
2
C master device generates a start condition. The start condition applies
when the SCL line is maintained at high and the SDA line is pulled down to low.
To generate a start condition in this I
2
C master, set IMTGMOD[2:0] to 0x0 (default) and write 1 to IMTG.
SDA (USI_DI)
SCL (USI_CK)
Start condition
5.3.3 Start Condition
Figure 18.
IMBSY is set to 1 while a start condition is being generated. When the start condition is generated, IMBSY
is reset to 0 and IMSTA[2:0] is set to 0x0. The I
2
C bus is busy from this point on.
Note: Other operations cannot be started before a start condition is generated.
(2) Sending slave address and transfer direction bit
After a start condition has been generated, send the address of the slave device to be communicated and a
transfer direction bit. I
2
C slave addresses are either 7-bit or 10-bit. This module uses an 8-bit transfer data
buffer to send the slave address and transfer direction bit, enabling single transfers in 7-bit address mode. In
10-bit mode, data is sent twice or three times under software control. Figure 18.5.3.4 shows the configura-
tion of the address data.