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

3.1.1. Nibble Positioning

 

Positioning of nibbles in the data string is a complex process. In order to correctly reconstruct the data string, the user must be very careful to read the correct nibble in the correct sequence.

Nibbles are read starting with the Least Significant Nibble (LSN) of the first byte in the string and ending with the Most Significant Nibble (MSN) of the last byte in the string. In other words, start by reading the LSN of the first byte followed by the MSN of the first byte, then the LSN of the second byte followed by the MSN of the second byte, and so forth.

When the "F" nibble is encountered, reconstruction of the literal character from the two nibbles following the "F" nibble follows the same rule. The first nibble read after the "F" nibble makes up the Least Significant Nibble (LSN) of the literal character. The second nibble read after the "F" nibble makes up the Most Significant Nibble (MSN) of the literal character. Two examples of these reconstruction methods are shown on the following page.

Example 1: Assume the "F" nibble is encountered as an LSN:

 

 

Figure 4: Example 1

1                     The LSN of the first byte is an "F" nibble indicating a literal byte follows.

2                     The MSN of the first byte (next nibble read) makes up the LSN of the literal character.

3                     The LSN of the second byte (next nibble read) makes up the MSN of the literal character.

4                     The character is reconstructed as "54" HEX or ASCII "T".

 

Example 2: Assume "F" nibble is encountered as an MSN:

 

 

Figure 5: Example 2

1                     The MSN of the first byte is an "F" nibble, indicating a literal byte follows.

2                     The LSN of the second byte (next nibble read) makes up the LSN of the literal character.

3                     The MSN of the second byte (next nibble read) makes up the MSN of the literal character.

4                     The character is reconstructed as a "54" HEX or ASCII "T".