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13.5
13.5.2 Transmission Interrupt Generation and Flag Set Timing
UART Interrupts
MB90560 series
CHAPTER 13 UART
A transmission interrupt is generated when the next piece of data is ready to be written
to the output data register (SODR0/1).
I
Transmission Interrupt Generation and Flag Set Timing
The transmission data empty flag bit (SSR0/1: TDRE) is set to “1” when data written to the
output data register (SODR0/1) is transferred to the transmission shift register, and the next data
is ready to be written. TDRE is cleared to “0” when transmission data is written to SODR0/1.
Figure 13.5-2 shows the transmission operation and flag set timing.
Figure 13.5-2 Transmission operation and flag set timing
G
Transmission Interrupt Request Generation Timing
If the TDRE flag is set to “1” when a transmission interrupt is enabled (SSR0/1: TIE=1),
transmission interrupt requests (#38 and #40) are generated.
<Check>
A transmission completion interrupt is generated immediately after the transmission interrupts
are enabled (TIE=1) because the TDRE bit is set to “1” as its initial value. TDRE is a read-
only bit that can be cleared only by writing new data to the serial output data register
(SODR0/1). Carefully specify the transmission interrupt enable timing.
ST
D0~D7
SP
A/D
D2
D3
D5
D6
D4
ST
D0
D1
ST
D0
D2
D3
D1
D7
SP
SODR writing
[Operation modes 0 and 1]
A transmission interrupt occurs.
A transmission interrupt occurs.
[Operation modes 2]
SODR writing
A transmission interrupt occurs.
A transmission interrupt occurs.
TDRE
SOT output
D3
D4
D6
D7
D5
D0
D1
D2
D3
D4
D6
D7
D5
D0
D1 D2
TDRE
SOT output
: Start bit
: Data bit
: Stop bit
: Address/data selection bit