X.3 PAD Parameters

---

X.3 PAD parameters set the guidelines for how the PAD deals with different terminal emulations. You use X.3 PAD parameters to control such features as local echo and line feed insertions after carriage returns, to enable local editing, and to determine what service signals are forwarded to the user.

 
X.3 PAD Parameter Support

---

There are 22 standard X.3 PAD parameters that are recognized internationally. These parameters and the functions they control are described later in this section. There also exist national X.3 PAD parameters numbered higher than 22, but their definition varies from country to country. The Eicon Host PAD and Eicon Terminal PAD do not support these national parameters.

You should be aware that each of the 22 international X.3 PAD parameters has both mandatory and optional values. The Eicon Host PAD and Eicon Terminal PAD support all mandatory values (as defined in CCITT Recommendation X.3, 1984); they also support many of the optional parameter values. Network support, however, will vary. Consult your network manager for specifics.

 
How to Set X.3 PAD Parameters

There are several ways to set X.3 PAD parameters. You can set them using tpadcfg or tpadprof with the Eicon Terminal PAD, or using the Linux stty command with the Eicon Host PAD.

The initial values for the Eicon Terminal PAD are setup using either tpadcfg or tpadprof. The Eicon Host PAD initial values are set in the device configuration entry in the /etc/gettydefs file.

 
X.3 PAD Parameters

The table below shows the CCITT PAD Parameters.

 
X.3 PAD Parameters

---

This section describes all 22 international X.3 PAD parameters in numerical order, together with the functions they control. All parameters and their possible values are decimal numbers.

ASCII control characters (ASCII characters 0 through 31) are entered as key sequences, such as Ctrl-P. A table of ASCII control characters, their keyboard entry sequences, and their common mnemonic references appear in X.25 User-Facility Support and Code References.

Certain X.3 PAD parameters can be coded as the sum of their listed values. This allows you to specify several values simultaneously. Parameter 7, for example, which deals with response to a break signal, has a default value of 21. This is the sum of three of the previous values: 1 (send an interrupt packet), 4 (send an indication of a break), and 16 (discard data). The X.3 PAD parameters that can be coded this way are parameters 3, 6, 7, 13, and 20.

1:n Escape from data transfer

When you send or receive data, this parameter allows you to escape from Data Transfer mode (Terminal mode) and enter Command mode. Flow of data from the network is temporarily suspended.

2:n Echo

This parameter provides for all characters to be echoed on your screen in data and command mode as well as to be forwarded to the remote device.

3:n Selection of data forwarding signal

This parameter defines sets of characters that act as data forwarding signals.

Coding of parameter 3 can be a single value or the sum of any combination of values listed above. A useful combination would be value 126, which is the sum of the values 2 through 64 (2+4+8+16+32+64 = 126). This would allow you to use any control character as the data forwarding signal.

Note: These characters are included in the forwarded data packet.

4:n Selection of idle timer delay

This parameter specifies the value of an idle timer used for data forwarding.

5:n Auxiliary Device Control

This parameter was originally designed to give control of the data flow to the PAD when it was dealing with high-speed input devices which could overflow its processing capacity. This is no longer necessary, since PADs provide buffering services automatically.

6:n Control of service signals

This parameter determines whether or not PAD service signals are to be transmitted by the PAD to the DTE (terminal). It also governs the use of Extended Service Signals, as well as the language in which service signals are displayed.

Note: For Extended Service Signals to be available, you must specify the languages you want to use.

7:n Procedure on receipt of break signal

This parameter specifies the operation upon entry of a break character.

Coding of parameter 7 can be a single value or the sum of any combination of values listed above. The default value (21) is the sum of 16 + 4 +1.

8:n Discard data

This parameter allows the PAD to discard data. It is permanently set to 0 (normal delivery to terminal) and cannot be directly modified, even in Command mode. You can, however, arrange for data to be discarded after a break signal if you set X.3 parameter 7 to 16.

9:n Carriage return padding

This parameter provides for the automatic insertion of a time delay referred to as a padding character into the character string after a carriage return. This allows for a printing mechanism to perform the carriage return function properly.

10:n Line folding

This parameter determines the maximum number of characters that can be printed or displayed on each line on your terminal. If more characters are entered, a new line will be started automatically.

11:n Communication speed

This parameter originally specified the speed of data transmission. You can set it to one of the values below if you are dealing with a host computer that needs to check this parameter when you first connect. However, this is a formality and will not affect the speed of your X.25 link.

12:n Flow control of the PAD by the workstation

This parameter allows for flow control of received data using X-ON and X-OFF characters. The X-ON character is DC1 (Ctrl-Q) and the X-OFF character is DC3 (Ctrl-S).

13:n Line Feed insertion after Carriage Return

This parameter instructs the workstation to routinely insert a Line Feed (LF) into the data stream after each appearance of a Carriage Return (CR) character.

Coding of parameter 13 can be a single value or the sum of any combination of values listed above.

14:n Linefeed padding

This parameter provides for the automatic insertion of padding characters, by the PAD, to allow for a time duration delay after each linefeed character. This allows a printing mechanism to correctly perform a line feed.

15:n Editing

This parameter allows you to perform local editing after a connection is made with the host. If you enable local editing (set parameter 15 to 1), you can correct any data buffered locally, rather than sending it across the network to the host for later correction. When local editing is allowed, the workstation monitors for characters which have been assigned per 16 (Character delete), 17 (Line delete), and 18 (Line redisplay).

Local editing cannot be enabled unless the idle timer (parameter 4) is set to 0.

16:n Character delete

This parameter lets you specify which ASCII character will delete the previously typed character from the buffer (provided local editing has been enabled).

17:n Line delete

This parameter lets you specify which ASCII character will delete the previously typed line from the buffer (provided local editing has been enabled).

18:n Line redisplay

This parameter lets you specify which ASCII character will redisplay the previously typed line (provided local editing has been enabled).

19:n Editing service signals

This parameter specifies what service signal to send to the terminal once the editing functions described by Character Delete, Line Delete, and Line Display characters (parameters 16, 17, and 18).

20:n Echo mask

This parameter specifies the characters from the workstation for which the PAD is to echo back to the DTE (terminal). The echo mask applies only when parameter 2 (echo) is set to 1.

Coding of parameter 20 can be a single value or the sum of any combination of values listed above. If parameter 5, 12 or 22 is set to a non-zero value, then X-ON (DC1) and X-OFF (DC3) are not echoed.

21:n Parity treatment

Not necessary for a software PAD, since an asynchronous signal is not being generated. Parameter 21 is permanently set to 0 and does not influence parity.

If your application generates parity signals, however, then the PAD will also generate them and will incorporate them into the packets it transmits. In this case the PAD will also remove parity signals from incoming packets before sending the data to your application.

22:n Page wait

The workstation will be able to suspend the transmission of additional characters after a specified number of linefeeds have been received. No further data will be transmitted until the page wait condition is canceled.

The workstation will cancel the page wait condition and resume normal transmission on receipt of an X-ON character (Ctrl-Q).