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 vali d
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