Appendix B – CnC interfACe protoCol
HPR130XD Auto Gas – 806330 Revision 1 b-27
Serial interface guidelines
Checksum
The protocol used for the serial interface between the Hypertherm system and the CNC contains a checksum on the
message being sent. The checksum should be validated for each message to ensure the information is not corrupted.
Message retries
We recommend retrying a message if the original message was not acknowledged by the system. This is especially
important when the high-frequency ignition is active. The high-frequency ignition can be active for up to 1 second and
can corrupt serial communications. It is important to space the retries so that the system can handle an interruption in
serial communications for up to 1 second.
Another alternative to handling the high frequency ignition is to poll for the power supply state, using the GET_STATE
command. If the state is (5 – Pilot arc) then stop serial communications until the state is no longer (5 – Pilot arc).
Cable shielding
We have chosen to use metal shell DB style machine/serial interface cables on some on the newer systems. One of the
reasons this type of cable was selected is for their EMI shielding capabilities. It is important that integrity of the shielding
of this cable be maintained. The shielding provides protection from the high-frequency ignition system, if the cable
shields are not properly terminated then the protection is not as effective. This is best achieved by ensuring the shield
has a 360° termination provided on both end of the cables. Using a drain wire will not achieve the proper shielding.
Thecable should also be as short as possible with no coils.
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