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【简答题】
什么是比特率?什么是波特率? 比特率是一种数字信号的传输速率,它表示单位时间内所传送的二进制代码的有效位数,单位____用比特每秒____或千比特每秒____表示。 波特率是一种调制速率,也称波形速率。它是针对在模拟信道上进行数字传输时,从调制解调器输出的调制信号,每秒钟载波调制状态改变的次数。或者说,在数据传输过程中,线路上每秒钟传送的波形个数就是波特率,其单位为波特____。
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【单选题】Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply a...
A.
Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply access the information base via programs stored on the system. Personal computer (PC) users typically access the host through a modem (调制解调器). A PC software program serves as an intece (接口)between the server and a PC, allowing the user to operate through the online system and select different databases using a keyboard or a mouse.
B.
National and regional online systems usually have local telephone numbers that PC modems can call to access either a local information base or an indirect long-distance connection, thus reducing long-distance telephone fees. Some online systems allow users ’to copy large volumes of information onto a local memory storage device, which also reduces the time the user is connected to the online system.
C.
Besides offering a great number of different information based, ranging from full-text journal li- braries to reports of missing children, online services allow users to, for example, reserve airline tick- ets, buy stocks, purchase goods, and communicate with other users. In exchange for the service, users usually pay a monthly membership fee. They may also pay to connect to various databases on the service or to download information.
【单选题】ITU V90调制解调器(MODEM)______。
A.
下载速率是56kb/s，上传速率是33.6kb/s
B.
上下行速率都是56kb/s
C.
与标准X.25公用数据网连接，以56kb/s的速率交换数据
D.
时刻与ISP连接，只要开机，永远在线
【单选题】为了使下面的程序段能用来把DL中的二进制代码从高位到低位依次转换为ASCII码并存入 DI 设定的内存数据区，试问该程序段中NEXT 处应填入( )指令。 MOV CX，8 NEXT： MOV AL， DL AND AL， 1 ADD AL， 30H MOV [D1]，AL INC DI LOOP NEXT
A.
SHL DL, 1
B.
SHR DL，1
C.
ROL DL，1
D.
ROR DL，1
【单选题】调制解调器(Modern)的作用是( )。
A.
将数字脉冲信号转换成模拟信号
B.
将模拟信号转换成数字脉冲信号
C.
将数字脉冲信号与模拟信号互相转换
D.
为了上网与打电话两不误
【单选题】调制解调器(Modem)的功能是。
A.
将数字信号转换成模拟信号
B.
将模拟信号转换成数字信号
C.
兼有A和B的功能
D.
使用不同频率的载波将信号变换到不同的频率范围
【单选题】要把0~1V的模拟电压量化输出为3位二进制代码，若将其分为8段，并取量化电平Δ=2/15V，则量化误差为（ ）。
A.
2/15V
B.
3/15V
C.
1/15V
D.
1/8V
【单选题】对8位二进制代码“01101101”进行奇偶校验，正确的结果是 (21) 。
A.
经奇校验可表明代码正确
B.
经偶校验可表明代码正确
C.
经奇校验发现错误，且能纠错
D.
经偶校验发现错误，但不能纠错
相关题目：
【单选题】Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply a...
A.
Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply access the information base via programs stored on the system. Personal computer (PC) users typically access the host through a modem (调制解调器). A PC software program serves as an intece (接口)between the server and a PC, allowing the user to operate through the online system and select different databases using a keyboard or a mouse.
B.
National and regional online systems usually have local telephone numbers that PC modems can call to access either a local information base or an indirect long-distance connection, thus reducing long-distance telephone fees. Some online systems allow users ’to copy large volumes of information onto a local memory storage device, which also reduces the time the user is connected to the online system.
C.
Besides offering a great number of different information based, ranging from full-text journal li- braries to reports of missing children, online services allow users to, for example, reserve airline tick- ets, buy stocks, purchase goods, and communicate with other users. In exchange for the service, users usually pay a monthly membership fee. They may also pay to connect to various databases on the service or to download information.
【单选题】ITU V90调制解调器(MODEM)______。
A.
下载速率是56kb/s，上传速率是33.6kb/s
B.
上下行速率都是56kb/s
C.
与标准X.25公用数据网连接，以56kb/s的速率交换数据
D.
时刻与ISP连接，只要开机，永远在线
【单选题】为了使下面的程序段能用来把DL中的二进制代码从高位到低位依次转换为ASCII码并存入 DI 设定的内存数据区，试问该程序段中NEXT 处应填入( )指令。 MOV CX，8 NEXT： MOV AL， DL AND AL， 1 ADD AL， 30H MOV [D1]，AL INC DI LOOP NEXT
A.
SHL DL, 1
B.
SHR DL，1
C.
ROL DL，1
D.
ROR DL，1
【单选题】调制解调器(Modern)的作用是( )。
A.
将数字脉冲信号转换成模拟信号
B.
将模拟信号转换成数字脉冲信号
C.
将数字脉冲信号与模拟信号互相转换
D.
为了上网与打电话两不误
【单选题】调制解调器(Modem)的功能是。
A.
将数字信号转换成模拟信号
B.
将模拟信号转换成数字信号
C.
兼有A和B的功能
D.
使用不同频率的载波将信号变换到不同的频率范围
【单选题】要把0~1V的模拟电压量化输出为3位二进制代码，若将其分为8段，并取量化电平Δ=2/15V，则量化误差为（ ）。
A.
2/15V
B.
3/15V
C.
1/15V
D.
1/8V
【单选题】对8位二进制代码“01101101”进行奇偶校验，正确的结果是 (21) 。
A.
经奇校验可表明代码正确
B.
经偶校验可表明代码正确
C.
经奇校验发现错误，且能纠错
D.
经偶校验发现错误，但不能纠错
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