user manual

8XC251SA, SB, SP, SQ USER’S MANUAL
10-10
10.5.3 Reset Addresses
On reset, the SADDR and SADEN registers are initialized to 00H, i.e., the given and broadcast
addresses are XXXX XXXX (all don't-care bits). This ensures that the serial port is backwards-
compatible with MCS
®
51 microcontrollers that do not support automatic address recognition.
10.6 BAUD RATES
You must select the baud rate for the serial port transmitter and receiver when operating in modes
1, 2, and 3. (The baud rate is preset for mode 0.) In its asynchronous modes, the serial port can
transmit and receive simultaneously. Depending on the mode, the transmission and reception
rates can be the same or different. Table 10-3 summarizes the baud rates that can be used for the
four serial I/O modes.
10.6.1 Baud Rate for Mode 0
The baud rate for mode 0 is fixed at F
OSC
/12.
10.6.2 Baud Rates for Mode 2
Mode 2 has two baud rates, which are selected by the SMOD1 bit in the PCON register (Figure
12-1 on page 12-2). The following expression defines the baud rate:
10.6.3 Baud Rates for Modes 1 and 3
In modes 1 and 3, the baud rate is generated by overflow of timer 1 (default) and/or timer 2. You
may select either or both timer(s) to generate the baud rate(s) for the transmitter and/or the receiv-
er.
Table 10-3. Summary of Baud Rates
Mode
No. of
Baud Rates
Send and Receive
at the Same Rate
Send and Receive
at Different Rates
01 N/A N/A
1 Many
†
Yes Yes
22 Yes ?
3 Many
†
Yes Yes
†
Baud rates are determined by overflow of timer 1 and/or timer 2.
Serial I/O Mode 2 Baud Rate 2
SMOD1
F
OSC
64
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