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???
10/11/10 19:17
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#179055 - On Some SiLabs Parts (but not 'F020)
Responding to: ???'s previous message
On the SiLabs parts the INTx pin can be used as an input to a timer running the as the increment input to the timer when it is running in the COUNTER mode. If the timer counter register is pre-loaded with the top count then a single occurrance of an edge on the INTx pin can cause the timer to roll over and generate an interrupt if enabled. On some of the SiLabs parts there is a polarity selector between the INTx pin logic and the gating that takes this into the counter clock circuitry. If you keep the Tx pin high and then toggle the INTx pin you can achieve an equivalent to a high true interrupt function. Sometimes the ISR has to reset the counter back to the reload count for the next interrupt. If the timer can be used in hardware auto-reload mode then this latter step can be skipped.

Unfortunately you have indicated you are using the C8051F020 and so this mode with the polarity selection is not available to you. One processor series that does have this polarity control feature is the C8051F34x family. So if you have some flexibility to change your design to another part you may want to look into this. In the end though it may be simpler to use the comparator or the external inverter as Erik has pointed out.

Michael Karas


List of 17 messages in thread
TopicAuthorDate
Port 3 interrupt and input problem, Silicon Labs C8051F020            01/01/70 00:00      
   inconsistency in datasheet            01/01/70 00:00      
      Thank you            01/01/70 00:00      
         also            01/01/70 00:00      
            Clarification on answer            01/01/70 00:00      
               for this            01/01/70 00:00      
                  Confusing replies            01/01/70 00:00      
                     Not my confusion            01/01/70 00:00      
                        confused me            01/01/70 00:00      
                           confused me            01/01/70 00:00      
                              hm            01/01/70 00:00      
                                 the common method is ....            01/01/70 00:00      
                                    good            01/01/70 00:00      
                                 On Some SiLabs Parts (but not 'F020)            01/01/70 00:00      
                                    interrupt polarity on F020            01/01/70 00:00      
                                       Correct?            01/01/70 00:00      
                                          EIE2, EA and ISR            01/01/70 00:00      

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