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

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 NetLink is on-line, The Buffer Functions Menu or Command ^B01 are used 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 NetLink to re­transmit the block. In either case, NetLink will immediately release a block of data.

4                     If the polling device does not respond, NetLink will wait for the specified Transmit Delay period, then retransmit the block and again wait for a response. NetLink will continue to retransmit the block until a response is received, or the user-specified number of Transmit Attempts is exhausted. The Transmit Delay and Transmit Attempts are defined via the port configuration menu for the port that will transmit the data. Port Configuration is described in Section 4.4 of the NetLink User's Guide.

 

5. When command ^B02 is invoked and there are no more blocks to be sent, NetLink 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.

If Command ^B30 is invoked to end the data release session, the same "END DATA" block is sent. In this case, however, the unit does exit read mode after the block is sent.