參數(shù)資料
型號: AT89LP52-20AU
廠商: Atmel
文件頁數(shù): 73/117頁
文件大小: 0K
描述: IC MCU 8051 8K FLASH SPI 44TQFP
標(biāo)準(zhǔn)包裝: 160
系列: 89LP
核心處理器: 8051
芯體尺寸: 8-位
速度: 20MHz
連通性: EBI/EMI,I²C,SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,POR,PWM,WDT
輸入/輸出數(shù): 36
程序存儲器容量: 8KB(8K x 8)
程序存儲器類型: 閃存
RAM 容量: 256 x 8
電壓 - 電源 (Vcc/Vdd): 2.4 V ~ 5.5 V
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 44-TQFP
包裝: 托盤
59
3709D–MICRO–12/11
AT89LP51/52
14.1
Multiprocessor Communications
Modes 2 and 3 have a special provision for multiprocessor communications. In these modes,
9data bits are received, followed by a stop bit. The 9th bit goes into RB8. Then comes a stop bit.
The port can be programmed such that when the stop bit is received, the serial port interrupt is
activated only if RB8 = 1. This feature is enabled by setting bit SM2 in SCON.
The following example shows how to use the serial interrupt for multiprocessor communications.
When the master processor must transmit a block of data to one of several slaves, it first sends
out an address byte that identifies the target slave. An address byte differs from a data byte in
that the 9th bit is “1” in an address byte and “0” in a data byte. With SM2 = 1, no slave is
interrupted by a data byte. An address byte, however, interrupts all slaves. Each slave can
examine the received byte and see if it is being addressed. The addressed slave clears its SM2
bit and prepares to receive the data bytes that follows. The slaves that are not addressed set
their SM2 bits and ignore the data bytes. See “Automatic Address Recognition” on page 61.
The SM2 bit can be used to check the validity of the stop bit in Mode 1. In a Mode 1 reception, if
SM2 = 1, the receive interrupt is not activated unless a valid stop bit is received.
14.2
Baud Rates
The baud rate in Mode 0 depends on the value of the SMOD1 bit in Special Function Register
PCON.7. If SMOD1 = 0 (the value on reset) and TB8 =0, the baud rate is 1/4 of the system fre-
quency in Fast mode. If SMOD1 = 1 and TB8 = 0, the baud rate is 1/2 of the system frequency,
as shown in the following equation:
:In Compatibility mode the baud rate is 1/6 of the system frequency, scaling to 1/3 when
SMOD1 = 1.
The baud rate in Mode 2 also depends on the value of the SMOD1 bit. If SMOD1 = 0, the baud
rate is 1/32 of the system frequency. If SMOD1 = 1, the baud rate is 1/16 of the system fre-
quency, as shown in the following equation:
14.2.1
Using Timer 1 to Generate Baud Rates
Setting TB8 = 1 in Mode 0 enables Timer 1 as the baud rate generator. When Timer 1 is the
baud rate generator for Mode 0, the baud rates are determined by the Timer 1 overflow rate and
the value of SMOD1 according to the following equation:
Mode 0 Baud Rate
TB8 = 0
2
SMOD1
4
--------------------
System Frequency
×
=
Mode 0 Baud Rate
TB8 = 0
2
SMOD1
6
--------------------
System Frequency
×
=
Mode 2 Baud Rate
2
SMOD1
32
--------------------
System Frequency
×
=
Mode 0 Baud Rate
TB8 = 1
2
SMOD1
4
--------------------
(Timer 1 Overflow Rate)
×
=
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