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Chapter 3.  Communications Operations of the BHT-100Q/100B
[ 2 ] Control Characters
The control characters are classified into two groups:  transmission control characters
and text control characters.
(1)  Transmission control characters
The transmission control characters listed below are used to compose transmission
control sequences in phases 1 through 3.
Symbol
Value
Meaning
Function
EOT
04h
End Of Transmission
Releases a data link (Phase 3).
Requests abort of transmission
(Phase 2).
ENQ
05h
Enquiry
Requests establishment of a data link
(Phase 1).
Prompts the receiver to respond to
the sent text (Phase 2).
ACK
06h
Acknowledge
Acknowledgment response to ENQ
(Phase 1).
Acknowledgment response to text
(Phase 2).
Acknowledgment response to EOT
(Phase 3).
NAK
15h
Negative Acknowledge
Negative acknowledgment response
to ENQ (Phase 1).
Negative acknowledgment response
to text (Phase 2).
  Transparency
The BHT uses the non-transparent mode which handles the control characters and
codes (e.g., STX, ETX, and SOH) as starting or ending markers and does not allow
them to be transmitted as normal data in the transmission texts.