Condition Code

Enhanced Definition

A Condition Code (CC) is a numeric status indicator set by the CPU, an operating system service, or an application program to reflect the outcome of an operation or the completion status of a job step. In z/OS, it is primarily used to control the flow of execution in JCL and to manage program logic in assembler language.

Key Characteristics

- Numeric Value: Typically a small integer. For CPU instructions, it's a 2-bit value (0-3) stored in the Program Status Word (PSW). For JCL job steps, it can range from 0 to 4095.
- CPU Instruction CC: Set automatically by most CPU instructions (e.g., arithmetic, logical, I/O) to indicate results like zero, positive, negative, overflow, or I/O status.
- JCL Step CC: Represents the return code from a batch program or utility executed within a job step, indicating success (typically 0) or various levels of failure or warning.
- System/User Defined: Can be set by the z/OS operating system, utility programs (e.g., IDCAMS, IEBGENER), or explicitly by user application programs (e.g., COBOL GOBACK with a RETURN-CODE value).
- Conditional Execution: Used extensively in JCL with the COND parameter or IF/THEN/ELSE statements to determine whether subsequent job steps should be executed.
- Program Status Word (PSW): The CPU's condition code is a field within the PSW, which is a critical control block for the CPU's state.

Use Cases

- JCL Conditional Processing: Preventing a critical update step from running if a preceding data validation or sort step failed (e.g., COND=(4,LT)).
- Assembler Language Branching: Using the CPU's condition code to branch to different routines based on the result of a comparison or arithmetic operation (e.g., BZ for branch if zero, BP for branch if positive).
- Error Handling in Batch Jobs: Detecting non-zero condition codes from utility programs (like IEBGENER or DFSORT) to log errors or trigger specific recovery actions.
- Application Program Flow: COBOL programs setting a specific RETURN-CODE value before GOBACK or STOP RUN to inform the calling JCL or program about the outcome of their execution.
- Job Restartability: Designing jobs where certain steps only execute if previous steps completed successfully, ensuring data integrity during restarts.

Related Concepts

Condition codes are fundamental to Job Control Language (JCL), providing the primary mechanism for conditional execution of job steps using the COND parameter or IF/THEN/ELSE constructs. At a lower level, the CPU's condition code is an integral part of the Program Status Word (PSW), directly influencing program flow in Assembler Language through conditional branch instructions. Application programs written in COBOL or PL/I often set a Return Code which z/OS translates into the job step's condition code.

Best Practices:

Meaningful Return Codes: Programs should set clear, documented return codes (e.g., 0 for success, 4 for warning, 8 for minor error, 12+ for severe error) to facilitate JCL logic and problem determination.
Strategic JCL COND Usage: Use the COND parameter or IF/THEN/ELSE statements judiciously in JCL to prevent dependent steps from executing if preceding steps failed, ensuring job integrity.
Document CC Meanings: Maintain documentation for non-zero condition codes issued by custom applications or specific utility programs, explaining their significance and required actions.
Test Conditional Logic: Thoroughly test JCL with various condition code outcomes (simulated or actual) to ensure the job stream behaves as expected under different success and failure scenarios.
Avoid Overly Complex COND Combinations: For complex conditional logic, prefer IF/THEN/ELSE JCL constructs over multiple, intricate COND parameters on EXEC statements for better readability and maintainability.