X PROG 753: Invalid data or parameter value
X PROG 753 means the host sent a 3270 data stream with a value the terminal couldn't accept. IBM lists three cases: a read command followed by data, a bad character set in Repeat to Address or Graphic Escape, and a bad attribute or character set in Start Field Extended, Modify Field or Set Attribute.
Other names for this code
Also written as PROG 753, PROG753, X PROG 753, 3270 PROG 753, program check 753, PROG 753 IMS, PROG 753 CICS, TN3270 PROG 753, PCOMM PROG753.
Also shown as PROG753 or X PROG753 in Personal Communications.
What it means
PROG 753 is about values. The order or command is one the terminal knows, but a value that goes with it isn't allowed. IBM's emulator documentation lists three situations.
A read command with data after it. Read Buffer, Read Modified and Read Modified All ask the terminal to send the screen back. They take nothing after the command byte. If the host sends more bytes behind a read command, the terminal treats it as an error.
A bad character set in RA or GE. Repeat to Address (RA) fills the screen with one character, and Graphic Escape (GE) draws one character from the alternate set. If the character set involved isn't valid, the terminal rejects the write.
A bad attribute in SFE, MF or SA. These orders carry type and value pairs for color, highlighting, character set, outlining and so on. A type the terminal doesn't support, or a value outside the allowed list for that type, gives PROG 753.
The last case is the one seen most often in practice. IBM APAR IC81881 describes PROG 753 in Personal Communications when an application sent an extended highlighting value of X'40' in a Start Field Extended order. That value isn't one of the defined highlighting values. APAR IT34578 describes PROG 753 in an IMS application caused by the emulator not handling field outlining.
Common causes
- An SFE, MF or SA order carries an attribute value that isn't defined, such as a blank (X'40') where a highlighting value should be. Hand-built screens and maps with a missing value are typical sources.
- The application uses an attribute the emulator doesn't support, such as field outlining or a color or highlighting type the session doesn't report.
- A read command was sent with extra data behind it.
- A Repeat to Address or Graphic Escape order uses a character set the terminal lacks.
- An emulator defect. IBM fixed at least one Personal Communications case (APAR IT34578) where the emulator, not the application, was at fault.
How to find the problem
- Write down the screen and the key that triggered it. PROG 753 is usually tied to one map or one field.
- Take a data stream trace and look at the attribute pairs after each SFE (X'29'), MF (X'2C') and SA (X'28') order. Check each type and value against the tables in GA23-0059. Highlighting is type X'41' and its defined values are X'00', X'F0', X'F1', X'F2', X'F4' and X'F8'.
- Check whether the session reported support for the attribute in its Query Reply. If it didn't, the application shouldn't send it.
- Look for a read command (Read Buffer, Read Modified or Read Modified All) followed by more bytes in the same output.
- Search the emulator vendor's fix list for PROG 753. If the trace shows valid data, the emulator may be the one at fault.
How to fix it
- For the user, press Reset and then Clear, and try again. Report the screen and transaction if it keeps happening.
- Correct the attribute value in the map or program. In CICS BMS and IMS MFS, check the attribute settings for highlighting, color and outlining on the field named in the trace and reassemble the map or format.
- Only send extended attributes the terminal reported in its Query Reply. In CICS, the TYPETERM options for extended data stream, color and highlighting should match what the emulator really supports.
- Send read commands on their own with nothing after them.
- If the data stream is valid, apply the emulator vendor's fix. For IBM Personal Communications, check APARs IC81881 and IT34578 against your level.
An extended-highlighting example
IBM APAR IC81881 describes a PROG753 case caused by an extended-highlighting value of X'40'. In this illustrative Start Field Extended order, that value is the item to investigate:
29 02 C0 60 41 40 29: Start Field Extended; 02: two attribute pairs C0 60: basic field-attribute pair 41 40: extended highlighting with the reserved value
On a small screen, swipe the table to read all columns.
| Extended highlighting value | Meaning |
|---|---|
| X'00' | Default |
| X'F0' | Normal |
| X'F1' | Blink |
| X'F2' | Reverse video |
| X'F4' | Underscore |
Other values are reserved in this attribute. This example does not diagnose every PROG753; compare the actual trace and your emulator version.
IBM references: IC81881: extended highlighting and IT34578: IMS field outlining. These APARs concern specific PCOMM versions and fixes; do not apply their compatibility settings to other emulators by assumption.
Trace checklist for the application team
Use Explain this screen to understand the visible code. Give the trace evidence to your application team for byte-level investigation.
Read this error in WND Terminal
For a visible X PROG 753 message, Explain this screen can help interpret the screen under IT’s configured AI policy. It does not establish the cause of a rejected host data stream. Preserve the exact status and follow the diagnostic steps in this article.
Try the WND Terminal sample with fictional data · 3270 emulator features and installation · 5250 emulator for IBM i
IBM documentation
IBM Personal Communications documentation. Use the documentation for your installed release.
This link opens the relevant IBM reference library or lookup instructions. Match the complete code and your installed product release; it is not a code-specific review.
Related codes
Questions
Why does PROG 753 appear in one emulator but not another?
Emulators differ in how strictly they check attribute values and which attributes they support. One may ignore a bad highlighting value, another rejects it with PROG 753.
Is PROG 753 an IMS problem or a CICS problem?
Neither in particular. It happens with any application that sends a bad value, and IBM has documented cases in both IMS applications and other z/OS applications.
What should I send to the programmers?
The transaction, the screen, the time and the emulator product and level. A data stream trace of the failing screen makes it much faster to find the bad value.