entPhysicalFirmwareRev 1.3.6.1.2.1.47.1.1.1.1.9

The vendor-specific firmware revision string for the physical entity. Note that if revision information is stored internally in a non-printable (e.g., binary) format, then the agent must convert such information to a printable format, in an implementation-specific manner. If no specific firmware programs are associated with the physical component, or if this information is unknown to the agent, then this object will contain a zero-length string.