3270 terminal screen protection

Under certain conditions, IMS avoids sending output to a 3270 terminal that could possibly destroy the operator's current work. IMS protects the screen so that you can safely enter data or control requests.

You can:

Set the screen mode to protect and:
- IMS successfully sends output to the screen.
- You press the Clear key and IMS responds by unlocking the keyboard.
- You or the application program perform a successful Copy function.
Requested the NEXTMSGP function (the PA3 key or a PF key so defined) when no output message was available.

The screen is not protected after you:

Press one of the following keys:
- Enter
- PA1 or PA2
- Any PF key (except a PF key defined as NEXTMSGP)
Operate either of the following devices:
- The selector light pen
- The ID card reader

Attention: If the screen is protected, an IMS shutdown checkpoint cannot complete.

During IMS system definition (using the TERMINAL and TYPE macros or ETO logon descriptors) you can specify that a 3270 screen be left in unprotected mode when IMS sends an output message to it. In unprotected mode, IMS can send output to the device at any time without requiring input from the terminal (an input message or a PA1 or PA2 action). IMS provides this option on a terminal-by-terminal or message-by-message basis. The terminal option of unprotected mode applies to all messages for that terminal. If you do not select unprotected mode, MFS-formatted messages leave the screen protected or unprotected on a message-by-message basis, and messages that bypass MFS leave the screen protected.

By allowing the terminal to be unprotected, IMS can continually update the 3270 display terminal with current information without requiring the terminal operator to initiate any action to receive output messages. Use this option only with terminals that require limited input and require the most current IMS output message.

To avoid losing data, press the PA3 key (if the PA3 key is not used for copy) before entering data. When you press the PA3 key, you put the terminal in protected mode, and you can enter data. After you enter the data, IMS returns the terminal to unprotected mode.