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Checksum calculator
Copyright 2004 EverFocus Elec. Corp.  http://www.everfocus.com
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I Introduction

This tool is used to calculate the checksum for EverFocus DVR commands.
It has two input methods to calculate the checksum as following sections.

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II Item input method

This method will automatically add length byte for you.
Input several items in the commands like:

Receiver ID:  in decimal digits, from 0 to 19383. Note 19383 is broadcast
              ID.
     Opcode:  in hexdecimal digits. Check DVR manual for opcode list.
       Data:  in hexdecimal digits. Different opcode will be followed by
	          different data bytes. Check DVR manual for details. If some
			  opcode doesn't need data, leave it blank.

After input all these items, click "Calculate checksum" button in the top
area or press "Enter" button to get the checksum result. All the data will
be shown at bottom result area. The checksum is the last hex digit.

Sample: Let us take example 2 in manual as sample here:
A packet that send "PAUSE" key to DVR (ID=4999) will be:
	0x85 (length)
	0x27 (Receiver ID high byte)
	0x07 (Receiver ID low byte)
	0x4B (Opcode = key)
	0x0C (Data1="pause"key)
	0x0A (Checksum)
Then just 
input 4999 in receiver ID textbox
input 4B in opcode text box
input 0C in data text box
press "Enter", You will get the result as below:

85 27 07 4b 0c 0a

where 0a is the checksum you need.

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III Direct input method

This method is for advanced user only.

You need to input everything in the textbox including the length byte.
Make sure all the bytes you input are in hex digits.

Click "Calculate checksum" button in "Direct input" area or press "Enter" 
button to get the checksum result. All the data will be shown at bottom 
result area. The checksum is the last hex digit.

Sample: Let us take example 2 in manual as sample here:
A packet that send "PAUSE" key to DVR (ID=4999) will be:
	0x85 (length)
	0x27 (Receiver ID high byte)
	0x07 (Receiver ID low byte)
	0x4B (Opcode = key)
	0x0C (Data1="pause"key)
	0x0A (Checksum)
Then just 
input 85 27 07 4B 0C in textbox in directinput area
press "Enter", You will get the result as below:

85 27 07 4b 0c 0a

where 0a is the checksum you need.