Home WTI User's Guides
cover
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

2.1. Compressed Binary Block Read Sequence

 

The binary block "read" commands are identical to the ASCII read commands. However, the sequence of the read operation is different. The binary block read sequence is as follows:

1                     Once the PollCat is on-line, Command ^B01 is sent to request the first block of data.

2                     When the entire block is received by the polling device, data is verified using the character count, ETX character or CRC code.

3                     If the polling device determines that data has been correctly received, Command ^B02 is sent to acknowledge the block and release the next data block. If the polling device determines that data has been corrupted during transmission, Command ^B06 is sent to the PollCat to re-transmit the block. In either case, PollCat will immediately release a block of data.

4                     If the polling device does not respond, PollCat will wait for the specified timeout period (see Command ^B14), then re­transmit the block and again wait for a response. PollCat will continue to re-transmit the block until a response is received, or the user-specified number of Re-Transmits (see Command ^B14) is exhausted.

5                     When command ^B02 is invoked and there are no more blocks to be sent, PollCat responds with a special block. This block has a block type byte of "FF" and contains a single record with the text "END DATA". The binary block method differs from the ASCII method in that this last "END DATA" message block must be acknowledged with a ^B02 command before the read command is terminated.

 

When Command ^B30 command invoked, the same "END DATA" block is sent. In this case, however, the unit does exit the read mode after the block is sent.