Envoy Application Programming Manual

Asynchronous Line Supervisor Protocol
Envoy Application Programming Manual—427159-001
10-3
Read-Only Mode
Default values for the TCHAR modifier are provided in Table 10-1.
You cannot specify termination and strip characters in your application through a
SETMODE command. For additional information on the TCHAR modifier, refer to the
Envoy Configuration and Management Manual.
Read-Only Mode
In read-only mode, Envoy keeps buffers available to receive incoming bytes from the
line. When the application calls READ, the saved bytes are passed from the Envoy
buffer to the application.
You can enable the read-only mode in either of the following ways:
•
Specify the READONLY modifier when issuing the ADD DEVICE command.
•
Call the SETMODE 16 procedure.
SETMODE 16 parm1.<13> = 0 normal
= 1 READONLY
In read-only mode, Envoy passes each byte to the Compaq CPU as it is received. The
Envoy asynchronous line supervisor driver code packs the data bytes into contiguous
form as each READ completes.
The initial READ byte-count determines the byte-count termination of subsequent
READs. The application must call HALTPOLL to terminate the READ.
Note. Characters that are stripped are not included in the read count.
Table 10-1. Default Values for Termination and Strip Characters
TCHAR Octal Value Meaning
TCHAR1 200 Strip zeroes.
TCHAR2 377 Strip idles
TCHAR3 4 Send interrupt on EOT
TCHAR4 3 Send interrupt on ETX
Note. n previous releases, Envoy read-only lines were also referred to as read-continuous,
because they were configured by using the READCONT modifier. The READCONT modifier
has now been replaced by the READONLY modifier (the READCONT modifier does not cause
an error). The read-only mode and the read-continuous mode are basically synonymous.
Note. Dedicated system buffers must be specified twice as large for read-only lines as for
normal lines.