Error Correction Mode (Ecm) - OKIDATA OF1000 Service Manual

2.1.06 Error Correction Mode (ECM)

The Okifax 1000 features Error Correction Mode (ECM). When communicating with a remote unit
that also has ECM, this feature provides error-free transmission.
What follows is an explanation of how ECM works.
· 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 PPS (Partial Page
Signal) 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 MCF (Message Confirmation) which requests the
transmit machine to transmit the next data block.
· If an error is detected by the receive machine, it transmits the frame number of the defective
frame back to the transmit machine in a signal called PPR (Partial Page Request).
· 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 (Message Confirmation).
· The next data block is then transmitted.
Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)
Service Guide OF1000
Chapter 2 Principles of Operation
Page: 19