Home WTI User's Guides
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1. Introduction
2. Binary Block Read Mode and Structure
2.1. Compressed Binary Block Read Sequence
2.2. Compressed Binary Block Structure
2.2.1. Data Block Structure
2.2.2. Record String Structure
3. Compression Decompression Methods
3.1. Table Decompression
3.1.1. Nibble Positioning
3.1.2. Record String Format
3.1.2.1. Data Decompression Considerations
3.1.3. Table Decompression Example
3.2. Space Compression
4. DLE Stuffing
5. The Cyclic Redundancy Check Option
5.1. Calculation
6. Other Binary Read Commands
6.1. Continuous Binary Block Read
6.2. Send Binary Information Block
7. Customer Service
PollCat NetLink B

3. Compression Decompression Methods

 

NetLink uses two types of compression; Space Compression and Table Compression.

The two methods combined will typically compress data to 60% or less of its original size. This is done without eliminating any fields or rearranging data in any way. Using the decompression methods, the data can be reconstructed to exactly match the original data received.

When data is received, NetLink does compression in two steps. First, the strings of spaces are compressed into single character representations, one character replacing many spaces. Next, the space compressed string is table compressed. This method uses a lookup table scheme to compress the 15 most commonly received characters into four bit half characters or "nibbles".

Decompression must be performed in the reverse order of compression. The data must first be table decompressed, and then space decompressed.