18 UNIVERSAL SERIAL INTERFACE (USI)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
18-29
Slave mode
USI_CK (SCPOL = 1, SCPHA = 1)
USI_CK (SCPOL = 1, SCPHA = 0)
USI_CK (SCPOL = 0, SCPHA = 1)
USI_CK (SCPOL = 0, SCPHA = 0)
USI_DI
USI_DO
Fetching received data
into shift register
D7 (MSB)
D0 (LSB)
D7 (MSB)
D0
8.2 Clock and Data Transfer Timing (MSB first)
Figure 18.
D1
Reserved (Do not set to 1.)
D0
SFSTMOD: Fast Mode Select Bit (for SPI master mode)
Selects Fast mode.
1 (R/W): Fast mode
0 (R/W): Normal mode (default)
In SPI master mode, either normal or fast clock mode can be selected using SFSTMOD. Setting SFST-
MOD to 0 (default) places the USI into normal mode and the USI generates the transfer clock by divid-
ing the T8 output by 2. Setting SFSTMOD to 1 places the USI into fast mode and the USI uses PCLK1
supplied from the CMU directly as the transfer clock. The fast mode does not use the T8.
The SPI slave mode uses the T8 output clock for generating the sampling clock.
USI SPI Master/Slave Mode Interrupt Enable Register (USI_SIE)
Register name Address
Bit
Name
Function
Setting
Init. R/W
Remarks
USI SPI Master/
Slave Mode
Interrupt
Enable Register
(USI_SIE)
0x300451
(8 bits)
D7–3 –
reserved
–
–
–
0 when being read.
D2
SEIE
Receive error interrupt enable
1 Enable
0 Disable
0
R/W
D1
SRDIE
Receive buffer full interrupt enable 1 Enable
0 Disable
0
R/W
D0
STDIE
Transmit buffer empty int. enable
1 Enable
0 Disable
0
R/W
Note: This register is effective only in SPI master and slave modes. Configure USI to SPI master/slave
mode before this register can be used.
D[7:3]
Reserved
D2
SEIE: Receive Error Interrupt Enable Bit
Enables interrupt requests to the ITC when an overrun error occurs.
1 (R/W): Enabled
0 (R/W): Disabled (default)
Set this bit to 1 to process overrun errors using interrupts.
D1
SRDIE: Receive Buffer Full Interrupt Enable Bit
Enables interrupt requests to the ITC when received data is loaded to the receive data buffer.
1 (R/W): Enabled
0 (R/W): Disabled (default)
Set this bit to 1 to read received data using interrupts.
D0
STDIE: Transmit Buffer Empty Interrupt Enable Bit
Enables interrupt requests to the ITC when data written to the transmit data buffer is sent to the shift
register (i.e. when data transmission begins).
1 (R/W): Enabled
0 (R/W): Disabled (default)
Set this bit to 1 to write data to the transmit data buffer using interrupts.