Hmmm..Where did you get that from? G90 is for absolute mode and the opposite of that is G91 for incremental mode. They donít have anything to do with the G71 canned cycle mode. Well they will affect the outcome of the code but relate nothing to a canned cycle. Well let me rephrase that. I have seen them on G-code system "A" under cutting cycle A but IIRC this was for threading and I donít recall seeing this for the 20 series control. I could be wrong.
Anyway G71 should be a valid code on your control but only when using G-code system A or B, not C. Attached is an example of a G71 cycle from the programming manual.