Using SNA Communications Server terminals

Overview

This topic describes the procedures to be followed when using SNA Communications Server (formerly VTAM, Virtual Telecommunications Access Method). SNA Communications Server supports the use of:

• IBM 3270s and compatible terminals
• IBM 3767 terminals
• Terminals supported through IBM's Network Terminal Option (NTO).

Each type of terminal that can be used through SNA Communications Server provides slightly different capabilities, responses, and default parameter settings. Read the section of this topic that corresponds to your terminal type.

Getting online

To connect to Model 204 through SNA Communications Server, follow these steps:

1. Connect to Model 204 by issuing commands to the SNA Communications Server Control Program. Check with your system administrator for the procedures specific to your site. These procedures might automatically log you on to Model 204.
2. After the connection has been established, the system unlocks the terminal keyboard. If you are not already logged on to Model 204, begin the session by entering the first input line, usually one of the following commands:

   LOGIN userid [account]

   or:

   LOGON userid [account]

   These commands are described in detail on the LOGIN or LOGON command wiki page.
3. After successfully logging in, you can enter an input line, as described in Input lines.

IBM 3270 terminals (IODEV=7)

This section summarizes the information needed to use IBM 3270s through SNA Communications Server.

Note: Model 204 translates all unprintable characters to question marks (?) for output to 3270 terminals, to avoid I/O errors.

Input lines

SNA Communications Server support is provided for two modes of operation: line-at-a-time and full-screen support. In full-screen mode, when Model 204 is prepared to accept input, it issues the prompt character (>) and unlocks the keyboard. The user can now enter an input line.

A physical input line cannot exceed 78 characters; however, using a line continuation character at the end of an input line causes Model 204 to treat the next line as a logical continuation of the previous one.

The user indicates that the line is complete and transmits the line by pressing the Enter key. No data is transmitted until Enter is pressed. The 3270 editing keys can be used to correct the line before Enter transmits it.

With the exception of the RTRVKEY setting, program function (PF) keys are supported by Model 204 only when the user accesses a screen formatted through the SOUL full-screen formatting feature (see Full-screen formatting). Otherwise, PF keys are not supported and cannot be used to enter data. Any line entered by means of a PF key is considered null, and any data entered is lost.

End-of-page pause

Model 204 pauses at the end of each output page and waits for the user to respond before continuing. This allows the user to examine the contents of the screen. Model 204 prompts with an end-of-page prompt (>), indented 25 spaces.

Valid user responses are:

• Enter a null line (Return). The terminal goes on to the next page.
• Press the attention key (PA1) or enter *CANCEL, C, or K, then press the Enter key. Unless an ON ATTENTION statement is in effect (see Attention interrupt feature), the current output and request are cancelled.
• Enter a backpage request (see Backpaging).
• Enter the next input line in anticipation of the next input prompt. The line cannot exceed 53 characters.

As discussed in Pausing, the user can enter only one line of anticipatory input at this time. If the terminal reaches the end-of-page pause for the next page of input, the saved input line is lost.

Attention key

The PA1 key serves as the attention key on IBM 3270 terminals, unless the attention key has been reassigned by the user through the FSATTN parameter.

Canceling the current request

When using SNA Communications Server, the evaluation of the current SOUL request can be canceled in one of the following ways:

• When the terminal is waiting for a response from Model 204, the user can press the attention key (PA1).
• When Model 204 is waiting for input from the terminal or is actively displaying output on the terminal, the user can press the attention key.

Note: When Model 204 is compiling a request or executing a command, the user cannot cancel the operation by pressing the attention key.

Logging out and disconnecting

To disconnect from Model 204, the user logs out (if the LOGOFF procedure is required at the installation) by entering either:

LOGOUT

or:

LOGOFF

The user can then disconnect completely from the system, reconnect to Model 204, or connect to a different application by following the specific procedures defined at the installation.

Screen-formatting parameters

The parameters listed in the following table apply to IBM 3270 terminals being used through SNA Communications Server.

The HDRCTL and PGSEP parameters are not listed because they are not used with IBM 3270 terminals.

Screen-formatting parameters for SNA Communications Server 3270s

Parameter	Meaning
INMRL	Maximum input line length for terminal
INCCC	Input continuation column
LOUTPB	Length of output page buffer
OUTMRL	Maximum output line length for terminal
OUTCCC	Output continuation column
OUTLPP	Number of lines per page, including headers and trailers
MODEL	Array of screen size parameters for the particular 3270 model
HDRCTL	Page formatting options

The values of the first five parameters, which determine the size of the screen, are established by the value of the MODEL parameter, which corresponds to the terminal model within the 3270 family. Model 204 automatically sets MODEL to the appropriate value for SNA Communications Server 3270s, but the user also can reset it.

Terminal model options

The following table shows the valid settings for MODEL, the corresponding 3270 terminal types, and the corresponding default values for the screen size parameters. The user can reset INCCC and OUTCCC to override the default values established by the MODEL parameter. The new settings remain in effect for the thread until the user logs out.

Valid MODEL settings for SNA Communications Server 3270s

MODEL	INMRL	INCCC	OUTMRL	OUTCCC	OUTLPP	3270 terminal type
1	78	78	80	80	11	Model 1
2	78	78	80	80	23	Model 2
3	78	78	80	80	31	Model 3
4	78	78	80	80	42	Model 4
5	130	130	132	132	26	Model 5

Output page buffer settings

Note: MODEL is reset only if the size of the output page buffer (LOUTPB) is large enough to hold the new screen size.

The minimum LOUTPB settings are shown in the following table.

MODEL	LOUTPB
0	1170
1	1170
2	2130
3	2770
4	3650
5	3774

TERMOPT parameter

TERMOPT consists of a series of switches that can be set independently and can be reset to the following values for 3270s (options can be summed):

0	SNA Communications Server input exception causes soft restart of user.
1	No soft restart of user.
2	Request exception response only (no definite response).
64	String LOGON is placed before the first logical line of the SNA Communications Server LOGMSG.

IBM 3767 and NTO terminals (IODEV=37)

This section summarizes the information needed to use IBM 3767s and the terminals supported by NTO through SNA Communications Server.

Note: The IODEV=37 setting is no longer supported as of Model 204 version 7.6.

Input lines

When Model 204 is ready to accept input, it issues the prompt character and unlocks the keyboard. For 3767s supported by NTO, the prompt is the underscore character (_), which is backspaced over immediately after it is printed. For Teletypes supported by NTO, the prompt is the question mark (?). Once the keyboard is unlocked, the user can enter a single input line, which cannot exceed the number of characters specified in the INMRL parameter.

Therefore, Model 204 treats the following as end-of-message characters:

Character	For...
NL, FF	3767 terminals
CR, LF, XON, XOFF	Teletypes and Teletype-compatible terminals

Pausing and canceling output

The system pauses at the end of each page of output if:

• OUTLPP (lines per page) parameter is positive.
• HDRCTL (header control) parameter has been set to 4.

Pausing at the bottom of the page allows the user to change the terminal paper or to cancel the current request, if too much output is being received. The system unlocks the keyboard at the bottom of each page to allow the user to enter a response. The user causes continuation of output by entering a null line (Return) or by entering any character.

If the user is receiving too much output, the attention key (BREAK or ATTN) can be pressed at any time. Unless an ON ATTENTION statement is in effect (see Attention interrupt feature), this cancels all output and aborts the currently running request. If a procedure is being executed at the time of the attention interrupt, all the input lines in the procedure are flushed, and the user is returned to command level. The terminal keyboard is then unlocked, and the terminal immediately signals that it is ready for input again.

Pressing the attention key while Model 204 is waiting for input causes the system to respond with an error message, after which it immediately prompts for input.

Parameter default values

The following table shows the parameter default values that apply to 3767s and NTO terminals being used through SNA Communications Server.

Parameter Default Values for 3767s and NTOs

Parameter	Meaning	Default
INMRL	Maximum input line length for terminal	80
INCCC	Input continuation column	72
LOUTPB	Length of output page buffer	0
OUTMRL	Maximum output line length for terminal	132
OUTCCC	Output continuation column	132
OUTLPP	Number of lines per page, including headers and trailers	56
PGSEP	Number of lines between output pages	2
HDRCTL	Page formatting options	0
TERMOPT	Terminal options	0

Resetting parameters

The settings of INMRL, INCCC, OUTMRL, and OUTCCC can be set individually on the first IODEV=37 CCAIN parameter line(s). They can be reset using the RESET command, but not to a value larger than the IODEV line setting, if any. If a value larger than an IODEV value is specified, Model 204 automatically changes it to the IODEV value.

HDRCTL consists of a series of switches that control the formatting of pages transmitted to the terminal. Each switch can be set independently of the others.

HDRCTL can be reset to the following values for 3767s and NTOs:

0	Normal headers (system header with date, time, and page number).
1	Suppress header 0 (system header with date, time, and page number).
2	Suppress the blank line that normally follows header 0 for nonrequest output.
4	Pause at the end of an output page. An additional line is added to each page, in addition to OUTLPP plus PGSEP, to receive a reply.

TERMOPT consists of a series of switches that can be set independently and can be reset to the following values for 3767s and NTOs:

0	Default.
1	No idles are transmitted in the output lines.
2	Terminal is always unlocked.
64	String LOGON is placed before the first logical line of the SNA Communications Server LOGMSG.

Note: A TERMOPT setting of 2 is required in order for Model 204 to send an XON character to Teletype and Teletype-compatible terminals.