【单选题】
同步时序电路和异步时序电路比较，其差异在于后者___。
A. 没有触发器
B. 没有统一的时钟脉冲控制
C. 没有稳定状态
D. 输出只与内部状态有关
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相关试题
【单选题】
一位8421BCD码计数器至少需要___个触发器。
【单选题】
某电视机水平-垂直扫描发生器需要一个分频器将31500HZ的脉冲转换为60HZ的脉冲，欲构成此分频器至少需要___个触发器。
A. 10
B. 60
C. 525
D. 31500
【单选题】
555定时器属于___
A. 时序逻辑电路
B. 组合逻辑电路
C. 模拟电子电路
【单选题】
54多谐振荡器可产生 ___
A. 正弦波
B. 矩形脉冲
C. 三角波
D. 锯齿波
【单选题】
脉冲整形电路有___。
A. 多谐振荡器
B. 施密特触发器
C. 555定时器
【单选题】
56石英晶体多谐振荡器的突出优点是___ 。
A. 速度高
B. 电路简单
C. 振荡频率稳定
D. 输出波形边沿陡峭
【单选题】
TTL单定时器型号的最后几位数字为___。
A. 555
B. 556
C. 7555
D. 7556
【单选题】
555定时器不可以组成___。
A. 多谐振荡器
B. 单稳态触发器
C. 施密特触发器
D. JK触发器
【单选题】
59以下各电路中，___可以产生脉冲定时。
A. 多谐振荡器
B. 单稳态触发器
C. 施密特触发器
D. 石英晶体多谐振荡器
【单选题】
555定时电路端不用时，应当___。
A. 接高电平
B. 接低电平
C. 通过0.01µF的电容接地
D. 通过小于500Ω的电阻接地
【单选题】
89S51的内部程序存储器与数据存储器容量各为多少？___
A. 64KB、128B
B. 4KB、64KB
C. 4KB、128B
D. 8KB、256B
【单选题】
89S51比89C51多出了哪个功能？___
A. 存储器加倍
B. 具有WDT工能
C. 多了一个8位输入/输出端口
D. 多了一个串行口
【单选题】
6在DIP40封装的8×51芯片里，复位RESET引脚的引脚编号是什么？___
【单选题】
7在DIP40封装的8×51芯片里，接地引脚与电源引脚的引脚编号是什么？___
A. 1、21
B. 11.31
C. 20、40
D. 19、39
【单选题】
9在12MHz始终脉冲的8051系统里，一个机器周期有多长？___
A. 1µs
B. 12µs
C. 1ms
D. 12ms
【单选题】
12下列哪个寄存器是8×51内的16位寄存器？___
【单选题】
14在8×51的输入/输出端口里，哪个输入/输出端口执行在输出功能时没有内部上拉电阻？___
【单选题】
8×51的P0采用哪种电路结构？___
A. 集电极开路式输出
B. 基极开路式输出
C. 发射机开路式输出
D. 图腾柱输出
【单选题】
17在8×51里，若要扩展外部存储器时，数据总线连接哪个输入/输出端口？___
【单选题】
点亮一般的LED所耗用的电流约为多少？___
A. 1~5µA
B. 10~20µA
C. 1~5mA
D. 10~20mA
【单选题】
19一般地，蜂鸣器属于哪种负载？___
A. 电阻性负载
B. 电感性负载
C. 电容性负载
D. 不导电负载
【单选题】
7405/7406的输出采用哪种电路结构？___
A. 集电极开路式输出
B. 基极开路式输出
C. 发射机开路式输出
D. 图腾柱输出
【单选题】
21在继电器中，NO接点是一种什么接点？___
A. 不使用接点
B. 不存在接点
C. 激磁后即开路的接点
D. 常开接点
【单选题】
22所谓2P的继电器，代表什么意思？___
A. 只有2个接点
B. 两相的负载
C. 两组电源
D. 2组c接点
【单选题】
23共阳极七段数码管显示器的驱动信号有何特色？___
A. 低电平点亮
B. 低电平不亮
C. 高电平点亮
D. 以上皆非
【单选题】
24在8×51的程序里，若要将某个输入/输出端口设置成输入功能，应如何处理？___
A. 先输出高电平到该输入/输出端口
B. 先输出低电平到该输入/输出端口
C. 先读取该输入/输出端口的状态
D. 先保存该输入/输出端口的状态
【单选题】
8×51提供几个外部中断和定时器/计数器中断？___
A. 2,2
B. 3,6
C. 2,3
D. 3,7
【单选题】
8×51的IP缓存器的功能如何？___
A. 设置中断优先级
B. 启动中断功能
C. 设置中断触发信号
D. 定义CPU的网址
【单选题】
28若要让采用低电平触发，则应如何设置？___
A. EX0=0
B. EX0=1
C. IT0=0
D. IT0=1
【单选题】
29在Keil µVision3里进行调试/仿真时，在哪里操作才能触动程序中断？___
A. 在Interrupt System
B. 在Cotorl Box对话框里
C. 直接单击魔术棒按钮即可
D. 直接按0键
【单选题】
30在8×51所提供的中断功能里，下列哪个优先级比较高？___
A. T1
B. RI/TI
C. T0
D. INT0
【单选题】
31在TCON缓存里，IE1的功能是什么？___
A. 触发 IE1中断
B. 指示IE1中断的标志
C. 提高IE1优先等级
D. 取消IE1中断
【单选题】
32在Keil C里，中断子程序与函数又何不同？___
A. 中断子程序不必声明
B. 函数不必声明
C. 中断子程序必须有形式参数
D. 中断子程序一定会有返回值
【单选题】
33若要同时启用INT0及INT1中断功能，则应如何设置？___
A. TCON=0×81
B. IE=0×85
C. IP=0×83
D. IE=0×03
【单选题】
35在8×51的Timer里，若使用Mode 0，其最大计数值为多少个机器周期？___
A. 65636
B. 8192
C. 1024
D. 256
【单选题】
36在12MHz的8×51系统里，哪一种方式一次可定时5ms？___
A. Mode 0及Mode 1
B. Mode 1及Mode 2
C. Mode 2及Mode 3
D. Mode3及Mode 1
【单选题】
37若要让Timer作为外部计数只用，应如何设置？___
A. Gate=0
B. Gate=1
C. C/=0
D. C/=1
【单选题】
39下列哪个不是8×51所提供的省电方式？___
A. PD方式
B. IDL方式
C. LP方式
D. 待机方式
【单选题】
89S51的看门狗有何作用？___
A. 重复执行程序
B. 找回遗失数据
C. 复位系统
D. 防止中毒
【单选题】
41若要启用WDT，则应依次填入WDTRST寄存器哪些数据？___
A. 0xe1、0xe2
B. 0xe1、0x1e
C. 0x1e、0xe1
D. 0x10、0x01
推荐试题
【单选题】
Which statement about command authorization and security contexts is true？___
A. If command authorization is configured， it must be enabled on all contexts.
B. The change to command invokes a new context session with the credentials of the currently
C. AAA settings are applied on a per-context basis
D. The enable. 15 user ang admins with chang to permission ha e dfferent command authorization levels pertontext
【单选题】
Which command do you enter to enable authentication for OSPF on an interface？___
A. router（config-if）#ip ospf message-digest-key 1 md5 CIS COPASS
B. router（config-if）#ip ospf authentication message-digest
C. router（config-if）#ip ospf authentication-key CISCOPASS
D. router（config-if）#area 0 authentication message-digest
【单选题】
What feature defines a campus area network？___
A. It has a single geographic location
B. It lacks external connectivity.
C. It has a limited number of segments.
D. It has limited or restricted Internet access
【单选题】
Which type of attack most commonly involves a direct attack on a network？___
A. :phishing
B. Trojan horse
C. denial of service
D. social engineering
【单选题】
What information does the key length provide in an encryption algorithm?___
A. the cipher block size
B. the hash bloc k size
C. the number of permutations
D. the packet size
【单选题】
How do you verify TaCACS+ connectivity to a device？___
A. You successfully log in to the device by using the local credentials
B. You connect via console port and receive the login prompt.
C. You connect to the device using SSH and receive the login prompt.
D. You successfully log in to the device by using ACS credentials
【单选题】
Which term best describes the concept of preventing the modification of data in transit and in storage？___
A. availability
B. confidentially
C. fidelity
D. integrity
【单选题】
Which loS command is used to define the authentication key for ntp？___
A. switch（config ）#ntp authentication-key 1 mds Clcs
B. switch（config ）#ntp authenticate
C. switch（config）#ntp trusted-key 1
D. switch（config）#ntp source 192.168.0.1
【单选题】
What is true about the cisco lOS Resilient Configuration feature ?___
A. The feature can be disabled through a remote session
B. There is additional space required to secure the primary cisco lOS image file.
C. The feature automatically detects image or configuration version mismatch.
D. Remote storage is used for securing files
【单选题】
When is the default deny all policy an exception in zone-based firewalls？___
A. when traffic terminates on the router via the self zone
B. when traffic traverses two interfaces in different zones
C. when traffic traverses two interfaces in the same zone
D. when traffic sources from the router via the self zone
【单选题】
.If an access port is assigned as an isolated port in a PVLAN， which network ports can it communicate with？___
A. promiscuous ports in the same PLVAN
B. isolated ports in the same PVLAN
C. all ports in the same PAVLAN at ILAR
D. all ports in the adjacent PVLAN
【单选题】
Which IPSEC mode is used to encypt traffic directly between a client and a server VPN endpoint？___
A. quick mode
B. transport mode
C. aggressive mode
D. tunnel mode
【单选题】
Which command do you enter to verify that a vpn connection is established between two endpoints and that the connection is passing traffic？ ___
A. Firewall#sh crypto session
B. Firewall#debug crypto isakmp
C. Firewall#tsh crypto ipsec sa
D. Firewall#sh crypto isakmp sa
【单选题】
which type of Pvlan port allows communication from all port types？___
A. isolated
B. in -line
C. community
D. promiscuous
【单选题】
Which command do you enter to configure your firewall to conceal internal addresses？___
A. no ip directed-broadcast
B. no ip logging facility
C. no proxy-arp
D. no ip inspect audit-trial
E. no ip inspect
F. route
【单选题】
Which feature defines a campus area network？ ___
A. It has a limited number of segments.
B. It has limited or restricted Internet access
C. It lacks ex1ternal connectivity.
D. It has a single geographic location
【单选题】
What technology can you use to provide data confidentiality data integrity and data origin authentication on your network？___
A. IPSec
B. Certificate Authority
C. IKE
D. Data
E. ncryption Standards
【单选题】
which standard is a hybrid protocol that uses oakley and skerne ke y exchanges is an ISAKMP framework？___
【单选题】
What is the actual los privilege level of User Exec mode？___
【单选题】
What is the effect of the asa command crypto isakmp nat-traversal？___
A. It opens port 500 only on the out side interface
B. It opens port 500 only on the inside interface
C. It opens port 4500 on all interfaces that are IPSec enabled
D. It opens port 4500 only on the out side interfac
【单选题】
Which Fire POWER preproce ssor engine is used to prevent SYN attacks？___
A. Inline normalization
B. IP Defragmentation
C. Ports can
D. etection
【单选题】
Which NAT type allows objects or groups to reference an IP address ？___
A. identity NAt
B. static NAT
C. dynamic
D. dynamic NAT
【单选题】
Which Auto NAT policies are processed first？___
A. Dynamic NAT with longest prefix
B. Dynamic NAT with shortest prefix
C. static NAT with longest prefix
D. static NAT with shortest prefix
【单选题】
Which feature allows a dynamic Pat pool to se lect the next address in the pat pool instead of the next port of an existing address？___
A. next IP
B. round robin
C. dynamic rotation
D. NAT address rotation
【单选题】
Which IPS detection method can you use to detect attacks that are based on the attackers IP address？___
A. anomally-based
B. policy-based
C. signature-based
D. reputation-based
【单选题】
Which type of encryption technology has the broadest platform support？___
A. software
B. middleware
C. file-level
D. hardware
【单选题】
Which type of address translation supports the initiation of comm unications bidirectionally ？___
A. multi-session PAT
B. dynamic NAT
C. dynamic PAT
D. static NAT
【单选题】
Which label is given to a person who uses existing computer scripts to hack into computers while lacking the expertise to write the own？___
A. script kiddy
B. white hat hacker
C. hacktivist
D. phreaker
【单选题】
What is the primary purpose of a defined rule in an IPS？___
A. to configure an event action that takes place when a signature is triggered
B. to define a set of actions that occur when a specific user logs in to the system
C. to configure an event action that is pre-defined by the system administrator
D. to detect internal attacks
【单选题】
Which option is the default valuce for the Diffie- Hell man group when configuring a site-to-site VPn on an asa device ？___
A. Group 1
B. Group 2
C. Group 5
D. Group 7
【单选题】
Which feature filters CoPP packets?___
A. access control lists
B. class maps
C. policy maps
D. route maps
【单选题】
Which command is used in global configuration mode to enable AAA？___
A. configure-model aaa
B. configure aaa-modelA
C. aaa new-model
D. aaa
E. XEC
【单选题】
Which statement about the given configuration is true？___
A. The single-connection command causes the device to establish one connection for all TACACS
B. The single-connection command causes the device to process one TacAcs request and then move to the next server
C. The timeout com mand causes the device to move to the next server after 20 seconds of TACACS inactive
【多选题】
What are two well-known security terms？___
A. phishing//网络钓鱼
B. ransomware //勒索软件
C. BPDU guard
D. LACP
E. hair-pinning
【多选题】
Which two commands must you enter to securely archive the primary bootset of a device___
A. router（config ）#secure boot-config
B. router（config）#auto secure
C. router（config）#secure boot-image
D. router（config）#service passw ord-encryption
【多选题】
Which two functions can SIEM provide ？___
A. correlation between logs and events from multiple systems
B. event aggregation that allows for reduced log storage requirements
C. proactive malware analysis to block malicious traffic
D. dual-factor authentication
E. centralized firewall management
【多选题】
Which two features of Cisco Web Reputation tracking can mitigate web-based threats？___
A. buffer overflow filterin dhsuowip
B. Bayesian filters
C. web reputation filters
D. outbreak filtering
E. exploit filtering
【多选题】
What are two challenges when deploying host- level IPS？ ___
A. The deployment must support multiple operating systems.
B. It is unable to provide a complete networ k picture of an attack.
C. It is unable to determine the outcome of e very attack that it detects
D. It does not provide protection for offsite computers
E. It is unable to detect fragmentation attacks
【多选题】
Which technology can be used to rate data fidelity and to provide an authenticated hash for data?___
A. file reputation
B. file analysis
C. signature updates
D. network blocking
【多选题】
Which two statements about host-based iPS solutions are true？___
A. It uses only signature-based polices
B. It can be deployed at the perimeter.
C. It can be have more restrictive policies than network-based IPS
D. it works with deployed firewall
E. It can generate alerts based on be havior at the de sto
