參數(shù)資料
型號: ADUC842BCP32-3
廠商: ANALOG DEVICES INC
元件分類: 微控制器/微處理器
英文描述: MicroConverter 12-Bit ADCs and DACs with Embedded High Speed 62-kB Flash MCU
中文描述: 8-BIT, FLASH, 8.38 MHz, MICROCONTROLLER, QCC56
封裝: 8 X 8 MM, LEAD FRAME, MO-220VLLD2, CSP-56
文件頁數(shù): 67/88頁
文件大小: 903K
代理商: ADUC842BCP32-3
ADuC841/ADuC842/ADuC843
Mode 3: 9-Bit UART with Variable Baud Rate
Mode 3 is selected by setting both SM0 and SM1. In this mode,
the 8051 UART serial port operates in 9-bit mode with a vari-
able baud rate determined by either Timer 1 or Timer 2. The
operation of the 9-bit UART is the same as for Mode 2, but the
baud rate can be varied as for Mode 1.
Rev. 0 | Page 67 of 88
In all four modes, transmission is initiated by any instruction
that uses SBUF as a destination register. Reception is initiated in
Mode 0 by the condition RI = 0 and REN = 1. Reception is
initiated in the other modes by the incoming start bit if REN = 1.
UART Serial Port Baud Rate Generation
Mode 0 Baud Rate Generation
The baud rate in Mode 0 is fixed.
Mode 0 Baud Rate
= (
Core Clock Frequency
/12)
Mode 2 Baud Rate Generation
The baud rate in Mode 2 depends on the value of the SMOD bit
in the PCON SFR. If SMOD = 0, the baud rate is 1/32 of the
core clock. If SMOD = 1, the baud rate is 1/16 of the core clock:
Mode 2 Baud Rate
= (2
SMOD
/32 × [
Core Clock Frequency
])
Modes 1 and 3 Baud Rate Generation
The baud rates in Modes 1 and 3 are determined by the over-
flow rate in Timer 1 or Timer 2, or in both (one for transmit
and the other for receive).
Timer 1 Generated Baud Rates
When Timer 1 is used as the baud rate generator, the baud rates
in Modes 1 and 3 are determined by the Timer 1 overflow rate
and the value of SMOD as follows:
Modes
1
and 3
Baud Rate
= (2
SMOD
/32 × (
Timer 1 Overflow Rate
)
The Timer 1 interrupt should be disabled in this application.
The timer itself can be configured for either timer or counter
operation, and in any of its three running modes. In the most
typical application, it is configured for timer operation in the
autoreload mode (high nibble of TMOD = 0010 binary). In that
case, the baud rate is given by the formula
Modes 1 and 3
Baud Rate
=
(2
SMOD
/32) × (
Core Clock
/ [256
TH1
])
Timer 2 Generated Baud Rates
Baud rates can also be generated using Timer 2. Using Timer 2
is similar to using Timer 1 in that the timer must overflow 16
times before a bit is transmitted/received. Because Timer 2 has a
16-bit autoreload mode, a wider range of baud rates is possible
using Timer 2.
Modes 1 and 2
Baud Rate
= (1/16) × (
Timer
2 Overflow Rate
)
Therefore, when Timer 2 is used to generate baud rates, the
timer increments every two clock cycles rather than every core
machine cycle as before. Thus, it increments six times faster
than Timer 1, and therefore baud rates six times faster are possi-
ble. Because Timer 2 has 16-bit autoreload capability, very low
baud rates are still possible.
Timer 2 is selected as the baud rate generator by setting the
TCLK and/or RCLK in T2CON. The baud rates for transmit
and receive can be simultaneously different. Setting RCLK and/
or TCLK puts Timer 2 into its baud rate generator mode as
shown in Figure 73.
In this case, the baud rate is given by the formula
Modes 1 and 3 Baud Rate
=
(
Core Clock
)/(16 × [65536
(
RCAP 2H, RCAP 2L
)])
CLK*
T2
PIN
TR2
CONTROL
(8TL2
(8TH2
RELOAD
EXEN2
CONTROL
TPIN
TDETECTOR
EXF 2
TIMER 2
NOTE: AVAILABILITY OF ADDITIONAL
RCAP2L
RCAP2H
OTIMER 2
2
16
16
RCLK
TCLK
RX
TX
0
0
1
1
1
0
SMOD
OTIMER 1
C/T2 = 0
C/T2 = 1
*CORE CLK IS DEFINED BY THE CD BITS IN PLLCON
0
Figure 73. Timer 2, UART Baud Rates
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