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CHAPTER 13 UART
13.5 Interrupt of UART
UART supports the interrupt-related error flag bit (ORFE), received data flag bit (RDRF),
and transmitted data flag bit (TDRE), and the following interrupt sources:
• When received data is sent from the reception shift register to the serial input data
register (SIDR). (Reception interrupt)
• When transmitted data is sent from the serial output data register (SODR) to the
transmission shift register. (Transmission interrupt)
■ Transmission Interrupt
When the SSD register is read and the output data is written into the SODR register, the data written into
the SODR register is transferred to the internal transmission shift register. When next data becomes
writable, the TDRE bit is set to "1", then an interrupt request to the CPU (IRQ5) is generated if the
transmission interrupt is enabled (SSD: TIE = 1).
■
Reception Interrupt
● When operating mode is 0, 1, or 3
When data is correctly input up to the stop bit, the RDRF bit is set to "1". If an overrun error or framing
error occurs, the ORFE bit is set to "1".
These bits are set when a stop bit is detected. If the reception interrupt is enabled (SSD: RIE = 1), an
interrupt request to the CPU (IRQ6) is generated.
● When operating mode is 2
For both RDRF and ORFE, data is received or transmitted with the final data bit (D8) set to "1", these flags
go on when the stop bit at the end is detected. However, when the framing error occurs, the flag goes on
regardless of the final data bit. An interrupt request to the CPU is generated when the flag goes on and the
input data becomes "1".
■
UART Interrupt Related Registers and Vector Table Addresses
Table 13.5-1 provides the registers relating to the UART interrupts and vector table addresses. For details
of the interrupt operation, see Section "3.4.2 Steps in the Interrupt Operation ".
Table 13.5-1 UART Interrupt Related Registers and Vector Table Addresses
Interrupt name
Interrupt level setting register Vector table address
Register Bit Upper digits Lower digits
IRQ5
ILR2 (007C
H
)
L51 (bit3) L50 (bit2)
FFF0
H
FFF1
H
IRQ6
ILR2 (007C
H
)
L61 (bit5) L60 (bit4)
FFEE
H
FFEF
H