DLE (Data Link Escape):
It is a character that shall change the meaning of one or more contiguously following characters. It can provide supplementary control, or permits the sending of data characters having any bit combination.
DC1, DC2, DC3 and DC4 (Device Controls):
These are the characters for the control of ancillary devices or special terminal features.
NAK (Negative Acknowledgement):
It is a character transmitted by a receiving device as a negative response to a sender. It is used as a negative response to polling message.
SYN (Synchronous/ Idle):
it is used by a synchronous transmission system to achieve synchronization when no data is being sent a synchronous transmission system may send SYN characters continuously.
ETB (End of Transmission Block):
This character indicates the end of a block of data for communication purpose. It is used for blocking data, where the block structure is not necessarily related to the processing format.
CAN (Cancel):
It indicates that the data that precedes it in a message or block should be disregarded usually because an error has been detected.
EM (End of Medium):
It indicates the physical end of a tape, surface (usually of a disk’s platter) or other medium or end of the required of used portion of the medium.
SUB (Substitute):
It is a substitute for a character that is found to be erroneous or invalid.
ESC (Escape):
It is a character intended to provide code extension in that it gives a specified number of continuously following characters an alternate meaning.
FS (File Separator):
This character is used as a file separator character.
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