18 UNIVERSAL SERIAL INTERFACE (USI)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
18-27
UTBSY switches to 1 when transmit data is written to the transmit buffer and reverts to 0 after both the
shift register and transmit buffer become empty.
D4
UPEIF: Parity Error Flag Bit
Indicates whether a parity error has occurred or not.
1 (R):
Error occurred
0 (R):
No error (default)
1 (W):
Reset to 0
0 (W):
Ignored
UPEIF is set to 1 when a parity error occurs. At the same time a receive error interrupt request is sent
to the ITC if UEIE/USI_UIE register is 1. Parity checking is enabled only when UPREN/USI_UCFG
register is set to 1 and is performed when received data is transferred from the shift register to the
receive data buffer. UPEIF is reset by writing 1.
D3
USEIF: Framing Error Flag Bit
Indicates whether a framing error has occurred or not.
1 (R):
Error occurred
0 (R):
No error (default)
1 (W):
Reset to 0
0 (W):
Ignored
USEIF is set to 1 when a framing error occurs. At the same time a receive error interrupt request is sent
to the ITC if UEIE/USI_UIE register is 1. A framing error occurs when data is received with the stop
bit set to 0. USEIF is reset by writing 1.
D2
UOEIF: 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
UOEIF is set to 1 when an overrun error occurs. At the same time a receive error interrupt request is
sent to the ITC if UEIE/USI_UIE register is 1. An overrun error occurs if the next reception is com-
pleted when URDIF is 1 and the receive data buffer (USI_RD register) is not read (an overrun error
occurs at the time stop bit has been received). To reset UOEIF, perform USI software reset (write 0x0 to
USIMOD[2:0]/USI_GCFG register) to initialize USI.
D1
URDIF: Receive Buffer Full Flag Bit
Indicates the receive data buffer status.
1 (R):
Data full
0 (R):
No data (default)
1 (W):
Reset to 0
0 (W):
Ignored
URDIF is set to 1 when data received in the shift register is sent to the receive data buffer (when receiv-
ing is completed), indicating that the data can be read. At the same time a receive buffer full interrupt
request is sent to the ITC if URDIE/USI_UIE register is 1. URDIF is reset by writing 1.
D0
UTDIF: Transmit Data Buffer Empty Flag Bit
Indicates the transmit data buffer status.
1 (R):
Empty
0 (R):
Data exists (default)
1 (W):
Reset to 0
0 (W):
Ignored
UTDIF is set to 1 when the transmit data written to the transmit data buffer is transferred to the shift
register (when transmission starts), indicating that the next transmit data can be written to. At the
same time a transmit buffer empty interrupt request is sent to the ITC if UTDIE/USI_UIE register is 1.
UTDIF is reset by writing 1.