Envoy Application Programming Manual

Asynchronous Line Supervisor Protocol
Envoy Application Programming Manual—427159-001
10-13
Line Action by Procedure Call
Line Action by Procedure Call
This subsection describes the asynchronous and simplex line-control sequences
transmitted because of calls to file-system procedures. It also describes the actions of
file-system procedures in response to line states and to the reception of text sequences,
as follows:
•
Effect of Line Characteristics on Usage of File-System Procedures on page 10-13
•
READ Procedure on page 10-14
•
READ Buffering on page 10-16
•
WRITE Procedure on page 10-17
•
WRITEREAD Procedure on page 10-17
•
CONTROL 11 and CONTROL 17 (Set DTR) on page 10-18
•
CONTROL 15 and SETMODE 15 (Break) on page 10-18
•
CONTROL 17 Procedure (Automatic Speed Detection) on page 10-20
Effect of Line Characteristics on Usage of File-System Procedures
The calls to file-system procedures are affected by the line characteristics set when
issuing the ADD DEVICE command. The line characteristics can be altered with the
SETMODE 16 procedure.
The effects of the line characteristics on the use of file-system procedures is summarized
in Table 10-8
through Table 10-10.
Table 10-8. File-System Procedures for Read-Only Versus Normal Read Lines
Line Type Usage of File-System Procedures
Read-Only WRITEREAD, WRITE, and CONTROL 15 return error 2 (operation not
allowed on this type of line).
Normal Read All appropriate file-system calls are permitted.
Table 10-9. Modem Signals and Full-Duplex Versus Half-Duplex Lines
Line Type
Usage of RTS
(Request to Send)
Usage of CD
(Carrier Detect)
Full-duplex Always on. Not used.
Half-duplex On only during
WRITE requests.
READ requests wait for CD (carrier detect) before
a READ is initiated.
READs terminate when the carrier drops.