Programmable Logic Controllers
5th Edition
ISBN: 9780073373843
Author: Frank D. Petruzella
Publisher: McGraw-Hill Education
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Expert Solution & Answer
Chapter 2, Problem 47RQ
Explanation of Solution
Comparison on volatile and non-volatile memory elements:
| Volatile memory elements | Nonvolatile memory elements |
| Volatile memory loses all its stored information when there is no power supply connected to it. | Nonvolatile memory can retain its stored information even when the power is accidentally or intentionally removed. |
| Here, the memory can be easily altered. | Here, the memory cannot be altered. |
| They have effects on the system performance... |
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Whentheuserenters!!,themostrecentcommandinthehistoryisexecuted.In the example above, if the user entered the command:
Osh> !!
The ‘ls -l’ command should be executed and echoed on user’s screen. The command should also be placed in the history buffer as the next command.
Whentheuserentersasingle!followedbyanintegerN,theNthcommandin the history is executed. In the example above, if the user entered the command:
Osh> ! 3
The ‘ps’ command should be executed and echoed on the user’s screen. The command should also be placed in the history buffer as the next command.
Error handling:
The program should also manage basic error handling. For example, if there are no commands in the history, entering !! should result in a message “No commands in history.” Also, if there is no command corresponding to the number entered with the single !, the program should output "No such command in history."
Activity No.
Activity
Time (weeks)
Immediate Predecessors
1
Requirements collection
3
2
Requirements structuring
4
1
3
Process analysis
3
2
4
Data analysis
3
2
5
Logical design
50
3,4
6
Physical design
5
5
7
Implementation
6
6
c. Using the information from part b, prepare a network diagram. Identify the critical path.
2. UNIX Shell and History Feature [20 points]
This question consists of designing a C program to serve as a shell interface that
accepts user commands and then executes each command in a separate process. A
shell interface gives the user a prompt, after which the next command is entered.
The example below illustrates the prompt osh> and the user's next command:
cat prog.c. The UNIX/Linux cat command displays the contents of the file
prog.c on the terminal using the UNIX/Linux cat command and your program
needs to do the same.
osh> cat prog.c
The above can be achieved by running your shell interface as a parent process.
Every time a command is entered, you create a child process by using fork(),
which then executes the user's command using one of the system calls in the
exec() family (as described in Chapter 3). A C program that provides the general
operations of a command-line shell can be seen below.
#include
#include
#define MAX LINE 80 /* The maximum length command */
{
int…
Chapter 2 Solutions
Programmable Logic Controllers
Ch. 2 - Prob. 1RQCh. 2 - What is the function of a PLC output interface...Ch. 2 - Prob. 3RQCh. 2 - Prob. 4RQCh. 2 - Prob. 5RQCh. 2 - Prob. 6RQCh. 2 - Prob. 7RQCh. 2 - Prob. 8RQCh. 2 - Prob. 9RQCh. 2 - Prob. 10RQ
Ch. 2 - Prob. 11RQCh. 2 - What are the advantage and the disadvantage of...Ch. 2 - With reference to PLC discrete input modules: a....Ch. 2 - Prob. 14RQCh. 2 - Explain the function of the backplane of a PLC...Ch. 2 - Prob. 16RQCh. 2 - Prob. 17RQCh. 2 - Prob. 18RQCh. 2 - What electronic element can be used as the...Ch. 2 - With reference to discrete output module current...Ch. 2 - What electronic element can be used as the...Ch. 2 - Prob. 22RQCh. 2 - Prob. 23RQCh. 2 - Prob. 24RQCh. 2 - Prob. 25RQCh. 2 - Prob. 26RQCh. 2 - Prob. 27RQCh. 2 - Prob. 28RQCh. 2 - Prob. 29RQCh. 2 - Explain the difference between a unipolar and...Ch. 2 - Prob. 31RQCh. 2 - In what two ways can the loop power for current...Ch. 2 - Prob. 33RQCh. 2 - Prob. 34RQCh. 2 - Prob. 35RQCh. 2 - Write a short explanation for each of the...Ch. 2 - Write a short explanation for each of the...Ch. 2 - Prob. 38RQCh. 2 - Prob. 39RQCh. 2 - Prob. 40RQCh. 2 - Prob. 41RQCh. 2 - Prob. 42RQCh. 2 - Prob. 43RQCh. 2 - Prob. 44RQCh. 2 - Prob. 45RQCh. 2 - Prob. 46RQCh. 2 - Prob. 47RQCh. 2 - What information is normally stored in the ROM...Ch. 2 - Prob. 49RQCh. 2 - Prob. 50RQCh. 2 - Prob. 51RQCh. 2 - Prob. 52RQCh. 2 - Prob. 53RQCh. 2 - Prob. 54RQCh. 2 - Prob. 55RQCh. 2 - Prob. 56RQCh. 2 - Prob. 57RQCh. 2 - Prob. 58RQCh. 2 - Prob. 59RQCh. 2 - Prob. 60RQCh. 2 - What is the function of a transducer?Ch. 2 - Prob. 62RQCh. 2 - Prob. 1PCh. 2 - Assume a thermocouple, which supplies the input to...Ch. 2 - With reference to I/O module specifications: a. If...Ch. 2 - Prob. 4PCh. 2 - Prob. 5PCh. 2 - Prob. 6P
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