OKIDATA OF2200, Руководство по обслуживанию

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Service Guide OF2200/2400/2600
Chapter 1 Principles of Operation
1.1.06 Error Correction Mode (ECM)
Error Correction Mode (ECM) provides error-free transmission when communicating with a remote unit
that also has ECM.
Here is an explanation of the ECM process.
· The transmit machine groups image data into blocks and transmits one block of data at a time to the
receive machine. At the end of each block, a Partial Page Signal (PPS) is transmitted.
· The receive machine stores the data block in memory and checks each frame within that block for
errors.
Modified Huffman assigns a binary code to consecutive recurring bits of white or black. The codes must
add up to a total of 1728 bits, which is the Main Scan Rate established by CCITT.
Modified Read uses a comparison technique. The line being coded is compared to the previous line and
differences are noted. Codes are then assigned to reflect the differences between the two lines.
· If no errors are detected, the receiver sends Message Confirmation (MCF). MCF requests the transmit
machine to transmit the next data block.
· If an error is detected by the receive machine, the receive machine will transmit the frame number of
the defective frame back to the transmit machine in a signal called Partial Page Request (PPR).
· The transmit machine will then re-transmit the frame to the receive machine as a Partial Page.
· The receive machine rechecks the Partial Page, and (if all frames are correct) the receive machine
transmits MCF.
· The next data block is transmitted.
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