Hypertherm HPR260 Manual Gas Preventive Maintenance Program Rev.5 - Manual (Page 269)

APPENDIX B – CNC INTERFACE PROTOCOL
b-24 HPR260 Auto Gas Instruction Manual
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. The
cable should also be as short as possible with no coils.
Application Notes
Transmitting extra characters at the end of a message, or transmitting while the plasma system is responding.
The original control board 041808 and power supply control software revision H and prior can sometimes “lock up”
when the power supply receives characters while it is transmitting. The reason for this is that the control system cannot
process interrupts fast enough. In some cases, when a receive and transmit interrupt occur very close together, the
system will miss one of the interrupts and will not process any more serial characters. Under normal conditions, this will
not be an issue. As long as you wait for a response to every command before transmitting the next command, the
problem will not occur. Also it is important not to include extra characters at the end of a command such as a carriage
return or line feed. These are not required and can cause problems.
Power supply control software revision P improves the capability of the system and will reduce the likelihood of
occurrence, but it can still happen. The new style control board 041909 has fixed the problem in hardware.