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Asynchronous Serial Port
11-5
11.2.3 Serial Port Transmit Data Register (SPTD, Offset 84h)
Software writes this register (Figure 11-4) with data to be transmitted on the serial port.
The transmitter is double-buffered, and the transmit section copies data from the transmit
data register to the transmit shift register (which is not accessible to software) before
transmitting the data.
Figure 11-3 Serial Port Transmit Data Register (SPTD, offset 84h)
The value of SPTD at reset is undefined.
Bits 15–8: Reserved
Bit 7–0: Transmit Data (TDATA)—This field is written with data to be transmitted on the
serial port. The THRE bit in the Serial Port Status register indicates whether there is valid
data in the SPTD register. To avoid overwriting data in the SPTD register, the THRE bit
should be read as a 1 before writing this register. Writing this register causes the THRE bit
to be reset.
15
70
Reserved
TDATA