Modem Responses; Low-Level Modem Command Syntax - HP 82718A Expansion Pod Reference Manual

-
Software Usage and Examples
Modem Responses
Modem responses identify certain conditions of modem operatlOn. All modem responses, which are placed
in the modem receive buffer for
t'10D I t·u:
to read, are preceded by the command character to allow you
to distinguish between the responses and incoming data. The
L (LONG)
command specifies whether the
responses are to be long or short. Long responses are spelled out, and short responses are a single hex digit
The responses, in the two lengths, are:
Long Short
Response Response
ABORT A
BAD ANS
B
BUSY
0
CONNECT
1
CONN LOST
8
FAIL
9
NO ANS
2
NO DIAL
3
OK
4
OV OV
RING
5
RING IN
7
•
See appendix D, "HP 8271 8A Errors and Responses", for the meanings of the responses, commands that •
report them, and the exact sequence of characters that will be reported.
While you are developing and debugging applications using the modem, the long responses are useful to
help monitor what is going on, and are self -documenting as well. In the final version of an application,
short responses are preferable. Data from the phone line and responses generated by the modem cannot
be put in the modem receive buffer simultaneously. When a response is placed in the buffer, the
incoming data flow is halted for the time needed to put it there. There is a possibility of data loss because
of this, depending on how fast the host is transmitting. Short responses reduce this time interval and the
possibility of data being lost; in addition, the program length will decrease slightly, and the program will
be able to process received data slightly faster.
Low-Level Modem Command Syntax
All low-level modem commands begin with a command character so the modem can distinguish between
data to be transmitted and commands to be processed. Also, when the modem reports a response, it puts a
command character before the response so you can distinguish between responses and incoming data.
The default command character is
%,
but you can change it to something different using the N
(NEW)
command. When the modem receives the command character from the HP-7 5, it interprets all characters
received between the command character and a carriage return as commands. The general syntax of a •
low-level modem command is as follows: the command character, any number of commands (together ..
with their parameters) separated by commas, and a carriage return. The carriage return may be preceded
by a comma if the comma is preceded by a recognized command. This syntax is shown below;
eM
symbolizes the command character (usually
~),
and
qB
the carriage return.
•
30