AT83C51SND1C_03 ATMEL [ATMEL Corporation], AT83C51SND1C_03 Datasheet - Page 134

• Manufacturer Part Number: AT83C51SND1C_03
• Description: Single-Chip Flash Microcontroller with MP3 Decoder and Human Interface
• Manufacturer: ATMEL [ATMEL Corporation]

Serial I/O Port
Mode Selection
Baud Rate Generator
Timer 1
134
AT8xC51SND1C
The serial I/O port in the AT8xC51SND1C provides both synchronous and asynchro-
nous communication modes. It operates as a Synchronous Receiver and Transmitter in
one single mode (Mode 0) and operates as an Universal Asynchronous Receiver and
Transmitter (UART) in three full-duplex modes (Modes 1, 2 and 3). Asynchronous
modes support framing error detection and multiprocessor communication with auto-
matic address recognition.
SM0 and SM1 bits in SCON register (see Figure 125) are used to select a mode among
the single synchronous and the three asynchronous modes according to Table 123.
Table 123. Serial I/O Port Mode Selection
Depending on the mode and the source selection, the baud rate can be generated from
either the Timer 1 or the Internal Baud Rate Generator. The Timer 1 can be used in
Modes 1 and 3 while the Internal Baud Rate Generator can be used in Modes 0, 1
and 3.
The addition of the Internal Baud Rate Generator allows freeing of the Timer 1 for other
purposes in the application. It is highly recommended to use the Internal Baud Rate
Generator as it allows higher and more accurate baud rates than Timer 1.
Baud rate formulas depend on the modes selected and are given in the following mode
sections.
When using Timer 1, the Baud Rate is derived from the overflow of the timer. As shown
in Figure 94 Timer 1 is used in its 8-bit auto-reload mode (detailed in Section "Mode 2
(8-bit Timer with Auto-Reload)", page 53). SMOD1 bit in PCON register allows doubling
of the generated baud rate.
Figure 94. Timer 1 Baud Rate Generator Block Diagram
CLOCK
SM0
INT1
PER
0
0
1
1
T1
GATE1
TMOD.7
TCON.6
TR1
SM1
0
1
0
1
÷ 6
Mode
TMOD.6
C/T1#
0
1
2
3
0
1
Description
Synchronous Shift Register
8-bit UART
9-bit UART
9-bit UART
(8 bits)
(8 bits)
TH1
TL1
Overflow
Baud Rate
Fixed/Variable
Variable
Fixed
Variable
÷ 2
SMOD1
PCON.7
CLOCK
T1
0
1
4109E–8051–06/03
To serial
Port