Chapter 3 Communications Operations of BHT
129
[ 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.
(2) Text control characters
The text control characters are used to format transmission texts. In the BHT-protocol, they include the
following headers and a terminator.
Symbol Value Meaning Function
SOH 01h Start Of Heading Indicates the start of heading text (Phase 2).
STX 02h Start Of Text Indicates the start of data text (Phase 2).
ETX 03h End Of Text Indicates the end of data text (Phase 2).
You may designate headers and a terminator with the protocol functions in BHTBASIC. If you designate
none of them in a user program, the BHT may apply those as listed above. Refer to the "BHT-BASIC
Programmer's Manual."
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