Envoy Application Programming Manual
Table Of Contents
- What’s New in This Manual
- About This Manual
- 1 Application Programming With Envoy
- 7 ADM-2 Multipoint Supervisor Protocol
- 8 TINET Multipoint Supervisor Protocol
- 9 Burroughs Point-To-Point Protocol
- 10 Asynchronous Line Supervisor Protocol
- A ASCII Character Set
- B ASCII to EBCDIC Code Conversion
- C File-System Procedures
- D Statistics Messages
- E S-Series Changes to Envoy
- NonStop™ Himalaya S-Series Server Architecture
- G-Series Migration Considerations
- CBSENSEON and CFSENSEON Modifiers
- LEOTRESYN and NOLEOTRESYN Modifiers
- Treatment of Characters After the Termination Character
- Number of SYN Characters
- DTR Drop
- Reporting of Parity Error
- Half-Duplex Support for Asynchronous Lines
- Controller Replacement
- SYSGEN and COUP
- Unit Numbers
- FDX Line Changes
- No Support for Auto-Call Unit
- Glossary
- Index
BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-25
READ-Type Bit
READ-Type Bit
The READ-type bit allows the application process to detect an aborted transmission
sequence from the supervisor station. The READ-type bit is located in MCW.1 (message
control word, bit 1). The states of the READ-type bit have the following meanings:
0 = "continuation READ just completed"
1 = "initial READ just completed"
A complete message transmission from a supervisor station typically consists of one or
more messages that end with ETB characters, followed by a final message ending with
an ETX character, followed by an EOT sequence. The supervisor station may abort a
transmission to a tributary station by sending an EOT sequence before the final message
is sent. The receipt of an EOT sequence by the tributary station causes Envoy to resume
monitoring the line for polling and selection sequences.
The supervisor station may then reselect the same tributary station and reinitiate the
message transmission from the beginning. The application process detects the aborted
transmission sequence and the reselection of the tributary station by checking the state
of the READ-type bit after each READ completion.
Example 5-7
shows the transmission sequence for an aborted transmission and the state
of the READ-type bit.
The application process should check the state of the READ-type bit after each READ
completion. If a transmission is already in progress with a particular station (that is, a
message ending with ETB was received) and the READ-type bit is found to be a 1, then
an EOT sequence has been received and the tributary station was reselected. The
application process should then disregard the messages received prior to the time that the
READ-type bit became a 1.
Example 5-7. Aborted Transmission Sequence and READ-Type Bits
Tributary Supervisor
State of READ type
bit at READ completion:
<--- sel addr n
MCW.<1> = 1 <--- message ending with---ETB aborted-
= 0 <--- message ending with---ETB transmission
= 0 <--- message ending with---ETB sequence
<--- EOT
-----------
<--- sel addr n
MCW.<1> = 1 <--- message ending with---ETB
= 0 <--- message ending with---ETB resent-
= 0 . transmission
= 0 . sequence
= 0 .
= 0 <--- message ending with---ETX