Quatech INTERBUS S manual

It is possible to process and/or check the below listed actions via the control and status bits.

Extending the 16 bit counting range: The internal counting range is 16 bits or a maximum value of 65535. Should the application require an extended count range the location-difference-integration method may be employed. This method uses the control system to store the interrogated counter value. Any new interrogated value will have the previously stored counter value subtracted from it. This value will then be added to an accumulated register value. It is assumed that the counter difference of the two interrogated values is smaller than 16 bits therefore overflows need not be considered.

Another method calculates the extended counter range via the underflow and overflow status bits. The interrogated value is either added or subtracted to the accumulation register depending upon the status of the overflow or underflow bits.

Set Counter Position: The presetting of the counter is possible via the CNT_SET bit. The desired preset is loaded into the data register and the CNT_SET bit is set from 0 to

1.The CNTSET_ACC bit will be set to 1 when the preset value is loaded into the count register.

Maintaining the Present Counter Position: The counter present value may be maintained or latched via the external Latch input. First the external latch must be enabled via the EN_LATEXT bit. Once the input is enabled, the data will be latched into the counter module upon a 0 to 1 transition. Upon completion of the latch process the external latch valid bit LATEXT_VAL will be set to 1.

Maintaining a Reference Point: The storage of a present counter value may also accomplished via the Index pulse from the encoder. First the index latch enable bit must be set, EN_LACT, to a value 1. The counter present value will be latched upon the low to high transition of the Index input. Upon completion of the data latch process the Index Latch Valid bit, LACT_VAL will be set to 1.

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