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• Should the PAD set the parity on characters going to the host?
• What if the user device is a graphics terminal and needs to swap
between normal characters mode and graphics mode?

It is not possible for all of these questions to have predetermined answers
given the profusion of computing devices with different characteristics.
The PAD therefore needs to have a number of parameter settings which
determine how it acts. These parameters are in fact dynamic and can
change the way the PAD acts from moment to moment.

2.2.1 PAD parameters and triple-X

The parameters are standardized in the CCITT X.3 recommendation, so
that all PADs are essentially the same. The following list shows some of
the X.3 parameters; the full list is given at the end of this chapter. All the
parameters are numeric and can take values from 0 to 255. Some of the
parameters are simple two-way switches, and for these a value of zero
means OFF or FALSE, and a value of a 1 means ON or TRUE.

Parameter Name Meaning

2 Echo If 1, then the PAD echoes keyboard
characters back to the screen. If 0, then
characters are not echoed. This parameter
would be set to 0 if the host were going
to echo characters.

3 Forward This defines when keyboard characters
buffered by the PAD are forwarded into
the network. For example, a value of 2
means forward the contents of the buffer
when Carriage Return is received.

9 Padding This defines a delay that the PAD should
make following the sending of a Carriage
Return. It is intended for use with slow
devices such as printers and printing
terminals.

10 Line fold This informs the PAD of the width of the
screen and indicates where the PAD
should insert newlines into the data
stream.

13 Linefeed This defines whether the PAD should
insert a Linefeed character after a
Carriage Return either from the user or
from the host, or for data echoed locally
by the PAD.

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