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A serial input/output (SIO) port provides a means for the system to communicate with external
devices. This device has a serial I/O (SIO) port that shares pins with port 2. This chapter describes
the SIO port and explains how to configure it. Chapter 6, "I/O Ports," explains how to configure
the port pins for their special functions. Refer to Appendix B for details about the signals dis-
cussed in this chapter.
7.1
SERIAL I/O (SIO) PORT FUNCTIONAL OVERVIEW
The serial I/O port (Figure 7-1) is an asynchronous/synchronous port that includes a universal
asynchronous receiver and transmitter (UART). The UART has one synchronous mode (mode 0)
and three asynchronous modes (modes 1, 2, and 3) for both transmission and reception.
TI
Interrupts
RI
SP_STATUS
The serial port receives data into the receive buffer; it transmits data from the port through the
transmit buffer. The transmit and receive buffers are separate registers, permitting simultaneous
reads and writes to both. The transmitter and receiver are buffered to support continuous trans-
missions and to allow reception of a second byte before the first byte has been read.
An independent, 15-bit baud-rate generator controls the baud rate of the serial port. Either XTAL1
or T1CLK can provide the clock signal. The baud-rate register (SP_BAUD) selects the clock
source and the baud rate.
Internal
Data
Bus
SBUF_RX
Receive Shift Register
SBUF_TX
Transmit Shift Register
Control Logic
SP_CON
Figure 7-1. SIO Block Diagram
SERIAL I/O (SIO) PORT
T1CLK
0
Baud Rate
XTAL1
1
Generator
SP_BAUD
MSB
CHAPTER 7
RXD
TXD
A2363-02
7-1
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