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english
BIS M-81_
Basic knowledge for the application
When sending data between the read/write head and the data carrier a procedure is re-
quired for recognizing whether the data were correctly read or written.
The processor is supplied with standard Balluff procedure of double reading and compar-
ing. In addition to this procedure a second alternative is available: CRC_16 data checking.
Here a test code is written to the data carrier, allowing data to be checked for validity at
any time or location.
Advantages of CRC_16
Advantages of double reading
Data checking even during the non-active phase
(data carrier outside read/write head zone).
No bytes on the data carrier need to be
reserved for storing a check code.
Shorter read times since each page is read only
once.
Shorter write times since no CRC needs to be
written.
Since both variations have their advantages depending on the application, the user is free
to select which method of data checking he wishes to use (see Configuration on 15 "Car-
rier data").
It is not permitted to operate the system using both check procedures!
Data security for
written and read
data
M-81_854610_E_0703.p65
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english
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To be able to use the CRC check method, the data carriers must be initialized. You either
use data crriers with the factory default data set (all data are 0), or you must initialize the
data carrier. There are two ways of doing this:
– Initializing the data carrier sing the "Init" function in Main Menu 2 (see 28).
– Writing to the data carrier using the special initialization command 'Z' (see 39).
If CRC_16 data checking is activated, a special error message is output to the interface when-
ever a CRC error is detected.
If the error message is not caused by a failed reed request, it may be assumed that one or
more memory cells on the data carrier is defective. That data carrier must then be replaced.
If the CRC error is however due to a failed write request, you must reinitialize the data carrier
in order to continue using it.
The checksum is written to the data carrier for each CRC block (corresponds to 16 bytes)
in 2-byte units of information. 2 bytes are lost for each CRC block, i.e. the CRC block con-
tains only 14 bytes of user information. This means that the actual usable number of bytes
is reduced (see 11 "Supported data carriers and memory capacity").
CRC_16 is factory deactivated.
BIS M-81_
Basic knowledge for the application
Data security for
written and read
data
CRC_16
Saving read data
Data which have been read from a data carrier which are now stored in the Handy Pro-
grammer can be saved in an EEPROM under a file name of your choice.
