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What TV Check Means

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PostPosted: Wed Apr 11, 2007 4:37 pm    Post subject: What TV Check Means Reply with quote

There are two types of parity checking on a Fanuc control. TV (Tape Vertical) parity is seldom used, and it's usually turned off on the "Setting" screen as previous posts have mentioned. TH (Tape Horizontal) parity is also used when reading tapes or loading programs electronically.

If you wanted to make a program that would pass the TV parity check, you must be sure that every block of the program has an EVEN number of characters. For example, if the block has an even number of characters, like:

G00G90X.5000 (12 characters)

...then you won't get a TV alarm when you read it in. If the block has an odd number of characters, like:

G00G90X-.5000 (13 characters)

..then your DNC software or your post processor will have to add a "space" character to the block so it really has 14 characters, and even number

Manually edited programs will have roughly half the blocks with even numbers of characters, and half the blocks will have odd numbers of characters. That means that every other block of your program will generate the TV alarm if you have it enabled. Our DNC software can be set to transmit the extra space characters automatically, so we can use TV parity if we want to (we don't, however).

If you notice, the programs that a Fanuc sends back to your PC always has an even number of characters. The odd numbered blocks will have the extra space at the end. If you manually edit one of those blocks, however, the block will not pass the TV check when you read it back in.

A totally different type of parity checking is TH (Tape Horizontal) parity. The TH alarm is generated when a wrong CHARACTER parity is read by the CNC. TH parity refers to the number of hole ACROSS a paper tape or (when downloading electronically) the number of binary bits in each character. Fanuc controls require even parity when reading ISO tapes (ASCII even parity) and odd parity when reading the old EIA tapes. Unlike TV parity checking, TH parity checking can not be turned off on a Fanuc. A TH alarm means that you have an illegal character in your program, or a problem with your paper tape reader or the RS232 transmission.
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