barcode reader in asp.net AVR PROJECT 6: ASTRODAT: A STAND-ALONE DATA ACQUISITION SYSTEM in Software

Generation Code 128A in Software AVR PROJECT 6: ASTRODAT: A STAND-ALONE DATA ACQUISITION SYSTEM

274 AVR PROJECT 6: ASTRODAT: A STAND-ALONE DATA ACQUISITION SYSTEM
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Note: 1) The power supply, once switched on, should not be switched off even between two sets of data acquisitions, when the system is not actually recording any data. Switching off the power will reset the circuit. When power is restored and the acquire switch is pressed again, the previous set of data acquisitions will be overwritten. The same precaution should be taken with the reset switch. It should be pressed only once after the power supply is given to the circuit. 2) In the field, the menu switch should not be pressed at all. This switch should be pressed only when the system has to be initialized at the base. Pressing this switch in the field (when the system is not interfaced with a computer) will hang the system and it will have to be reset. 3) While the data acquisition is in progress, if the activity LED starts flickering, then it indicates that the system memory (EEPROM memory) is full and no further samples can be recorded. Pressing the acquire switch now will not affect the status of the activity LED and the system has to be reset.
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Storing of data in the memory The data in the EEPROM (system memory) is stored as illustrated below. The format illustrated can be used for interpreting the data read from the EEPROM.
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MEMORY LOCATION DATA STORED
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0000 0001 0002 0003 0004 000B 000C 000D . . . (n) (n (n . . 1) 3)
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Time delay value Start tag Time tag Data tag . . . End tag Start tag set number set number . . set number time data
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2) (n
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Definition of individual tags 1) Start tag set number
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This tag is two bytes. Start tag is 1H (0001)b followed by the set number of 12 bits.
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BIT NUMBER DATA STORED
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15 14 13 12 11-0
0 0 0 1 Set number
ASTRODAT USER S GUIDE 275
2) End tag
set number This tag is also two bytes. The set number in this tag is the same as that in the corresponding start tag. The stop tag is 2H (0010)b.
DATA STORED
BIT NUMBER
15 14 13 12 11 0 3) Time tag
0 0 1 0 Set number
time The time tag is one byte which is followed by seven bytes of RTC data, which indicates the time at that the first observation in a set was recorded.
DATA STORED
BYTE NUMBER
1 2 3 4 5 6 7 8 4) Data tag
Time tag = 40H Year value Day value Month value Date value Hour value Minute Value Seconds value
data This tag is two bytes. The data tag is 8H, which is followed by 12 bits of actual sampled data.
DATA STORED
BIT NUMBER
15 14 13 12 11 0
1 0 0 0 Sampled data value
The sampled data value is interpreted as follows: Bit 11 is the sign. 1 indicates that the data value in bits 10 0 is in two s complement and the sampled value is negative. 0 indicates that the data value in bits 10 0 is to be read as it is, and the sampled value is positive.
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AVR PROJECT 7: SECURITY DONGLE
16.1 At a Glance
his chapter looks at ways of building security locks, also called dongles, for various applications. It covers:
1. 2. 3. 4. 5. 6. 7.
What security locks are Some ways in which security locks can be designed The algorithm for such locks Building the locks for the serial or the parallel port of the PC Designing a novel security lock for the PC parallel port PC driver for the lock Alternate designs
Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
278 AVR PROJECT 7: SECURITY DONGLE
16.2 Introduction
16.2.1 WHAT ARE SECURITY LOCKS
What are security locks and what are they used for Security locks in the context of computer hardware and software refers to a system of authorization that allows use of such hardware or software only to authorized users. As a computer user, you would be aware of login identification and associated password. Unless the correct password for a given login identification is entered, the computer system would not allow you to use the computer. This is an example of a software-based security lock of some sort. Similarly, when you purchase some expensive software, the software author or the supplier would want some control over the use of the software only to authentic customers and would like to restrict unauthorized proliferation of the software, as this leads to his loss of revenue. To implement this control, the author could provide you with a piece of hardware that is to be connected to the PC system on which the software is supposed to run. When you run the software on a computer, it would look for the presence of this hardware and if it fails to find it, the software would abort and terminate. On the contrary, when it finds the hardware present in the system, the software performs merrily. Typically, this additional piece of hardware is in the form of a small, sealed printed circuit board with circuitry and with a means of connecting it to the host computer. To allow the user to connect and disconnect this hardware easily, it is usually connected to the host parallel port or the RS-232 serial port, as these are the ports that are easily accessible to the user. Security locks to go on the USB also are available. The lock system works in the following manner:
1. The PC software sends some information to the lock and expects some return infor-
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