CAL Security and the 44701A

There is no security for CAL. If the CAL command is sent unwittingly, the calibration of the module will be trashed. However, there are some safeguards built in.An SWRITE or POKE to a CAL RAM location will not work unless the Mainframe and Module go through some security coding back and forth. This coding is automatically taken care of by the CAL command. The CAL command was purposely described only in the Service Manual.Here are alternatives to handle the situation:Consider putting an internal cal enable/disable switch between pin 4 of U600 and pin 21 of CAL RAM, U607. Pull pin 21 or cut trace. Run additional wire from pin 21 thru 50,000 ohm resistor to +5v pin 24 of U607.Do a CAL RAM checksum comparison using SREADS and WRITES to verify that it has not changed since last CAL.