Using SNA Communications Server terminals
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.
To connect to Model 204 through SNA Communications Server, follow these steps:
- 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.
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]
LOGON userid [account]These commands are described in detail on the LOGIN or LOGON command wiki page.
- 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.
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.
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
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.
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:
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.
The parameters listed in the following table apply to IBM 3270 terminals being used through SNA Communications Server.
|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.
|MODEL||INMRL||INCCC||OUTMRL||OUTCCC||OUTLPP||3270 terminal type|
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.
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).|
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.
IODEV=37 setting is no longer supported as of Model 204 version 7.6.
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:
|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.
|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|
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:
|1||No idles are transmitted in the output lines.|
|2||Terminal is always unlocked.|
Note: A TERMOPT setting of 2 is required in order for Model 204 to send an XON character to Teletype and Teletype-compatible terminals.