SM3E Data Sheet #:
TM054
Page 30 of 36 Rev: 04 Date: 01/26/11
Copyright 2011 The Connor-Winfield Corp. All Rights Reserved
Specifications subject to change without notice
SM3E Application Note on Interrupts
TheSM3/3Emodulesupportseightdifferentinterruptsandappearsin
INTR_EVENT (0x12)register.Eachinterruptcanbe
individuallyenabledordisabledviathe
INTR_ENABLE (0x13)register.Eachbitenablesordisablesthecorrespondinginterruptfrom
assertingtheSPI_INTpin.Interrupteventsstillappearinthe
INTR_EVENT (0x12)registerindependentoftheirenablestate.All
interruptsareclearedonce
INTR_EVENT (0x12)registerisread.Theinterruptsare
1. Anyreferencechangingfromavailabletonotavailable
2. Anyreferencechangingfromnotavailabletoavailable
3. M/SREFchangingfromactivitytonoactivity
4. M/SREFchangingfromnoactivitytoactivity
5. DPLLModestatuschange
6. Activereferencechange
7. LossofSignal
8. LossofLock
Interrupts and Reference change in Autonomous mode:Interruptscanbeusedtodeterminethecauseofareferencechange
inautonomousmode.LetusassumethatthemoduleiscurrentlylockedtoREF1.ThemoduleswitchestoREF2andSPI_INTpinis
asserted.Theuserreadsthe
INTR_EVENT (0x12)register.
Ifthemoduleisoperatinginautonomousnon-revertivemode,thecausecanbedeterminedfrombits4,5,6and7.Bit5issetto
indicateActivereferencechange.IfBit6issetthenthecauseofthereferencechangeisLossofActiveReference.IfBit7issetthen
thecauseofthereferencechangeisaLossofLockalarmontheactivereference.
Ifthemoduleisoperatinginautonomousrevertivemode,thecausecanbedeterminedfrombits1,4,5,6and7.Bit5issetto
indicateActivereferencechange.IfBit6issetthenthecauseofthereferencechangeisLossofActiveReference.IfBit7issetthen
thecauseofthereferencechangeisaLossofLockalarmontheactivereference.IfBit1issetthenthecauseofthereference
changeistheavailabilityofahigherpriorityreference.
Note:TheDPLLModeStatusChangebit(Bit4)isalsosettoindicateachangein
DPLL_STATUS (0x11)register,duringaninterrupt
causedbyareferencechange.Thedatain
DPLL_STATUS (0x11)registerhoweverisnotusefulindeterminingthecauseofa
referencechange.Thisisbecausebits0-2ofthisregisteralwaysreflectsthestatusofthecurrentactivereferenceandhencecannot
beusedtodeterminethestatusofthelastactivereference.
Interrupts in Manual Mode:Inmanualoperatingmode,whentheactivereferencefailsduetoaLossofSignalorLossofLockalarm,
aninterruptisgenerated.Forexample,incaseofaLossofSignal,bits4and6of
INTR_EVENT (0x12)registerwouldbesetto
indicateLossofSignalandDPLLModeStatusChange.Theusermaychoosetoreadthe
DPLL_STATUS (0x11)register,thoughin
manualmodebit6of
INTR_EVENT (0x12)registerisamirrorofbit0ofDPLL_STATUS (0x11)register.ThisholdstrueforaLossof
Lockalarm,wherebit7of
INTR_EVENT (0x12)registerisamirrorofbit1ofDPLL_STATUS (0x11)register.
Application Notes continued