The Overflow Flag is contained within the processor COM and OVF flags two-digit field. This field is defined as:
|Comparison Low (COML) flag||1|
|Comparison High (COMH) flag||0|
The Overflow Flag is not cleared at the beginning of an arithmetic operation, but is preserved. Therefore, it indicates overflow that has occurred at any time before or during a series of arithmetic operations or other interspersed non-arithmetic operations.
The Overflow Flag is stored in memory and reset by the Branch Communicate (OP = 30), Enter (OP = 31), Virtual Enter (OP = 35), and Hyper Call (OP = 62) instructions. It is also stored in memory and reset by the Interrupt and Hardware Call procedures.
The Overflow Flag is unconditionally restored from memory by the Return (OP = 63) and Virtual Branch Reinstate (OP = 93) instructions and conditionally restored from memory by the Exit (OP = 32) instruction.