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. Customer Service
PollCat Series

3.2. Space Compression

 

The space compression method uses a single character to represent a string of spaces. A space compression character is indicated by the eighth bit of the character set to "1". The remaining seven bits form a binary count of the number of spaces that the character is replacing. A maximum of 127 spaces can be represented by a single "FF" character. If the string of spaces is longer than 127, the "FF" character is followed by another space compression character that represents the remaining spaces.

Since space compression employs the eighth bit, this method can only be used with seven bit, ASCII data. Space compression cannot be used if the PBX Port is set for eight bits, no parity. The space compression bit (bit one) of the mode byte in the record header determines if space compression was used.

If space and table compression are both used, the space compression character will always be stored as a literal byte indicated by an "F" nibble. This is because the space compression character will never match a character in the table.