PRELIMINARY DATA SHEET - Rev 1.5
04/2008
11
ACD2203
LOGIC PROGRAMMING
TheACD2203 includes an interface for a two-wire
serialdatacontrolbusthatANADIGICShasdeveloped
forusewithitsdualPLLsynthesizers.Thisinterface
saves one connection between the host and the
dual synthesizer, compared to a standard CLOCK-
DATA-ENABLEthree-wireinterface.Theinterfaceis
optimizedforapplicationsinwhichthedualsynthesizer
isaslavereceiverdevice.Hoststhatconformtothe
I2C-BusSpecicationstandardcanbeusedtoprogram
adualPLLthatusesthisinterface.
Physical Interface
Thetwo-wire interface consists oftwodigital signal
lines,CLOCKandDATA.Thespeedoftheinterface
is nominally 400 kbits/sec. For data transmission,
the signal on the DATA line must be stable when
theCLOCKsignalishigh,andthestateofthedata
mustchangeonlywhiletheCLOCKsignalislow.A
logicleveltransitionontheDATAlineduringahigh
CLOCKsignalindicatesthebeginningorendofadata
transmission,asspeciedinthefollowingsectionsand
showninFigure21.
Addressing The Dual PLL
levelofaDCvoltageappliedtothispindetermines
thetwo-bitlogicstate,AS2andAS1toaddressthe
synthesizer. The software must be programmed
with the corresponding decimal equivalent of the
8b word selected, as shown in Table 7. Once the
dualPLLhasrecognizedtheStart indicator and the
correct address word, it sends an address
acknowledgement to the host by pulling the DATA
linelowforoneclockpulse.Thehostcanthenbegin
tosenddatatoprogramthedualPLL.
Sending Data
Afterreceivingtheaddressbyteacknowledgementfrom
thedualPLL,thehostbeginssendingprogramming
data in 8-bit words. The MSB is sent rst, and the
LSB last. Following the receipt of each 8-bit data
word,thedualPLLacknowledgesreceiptbypulling
the DATA line low for one clock pulse. The data
acknowledgementtellsthehostitmaysendthenext
dataword.ForthedualPLL,eachgroupofthreedata
words(24bitstotal)isasignicantblockofinformation
usedtoprogramoneoffourregisters,asdescribedin
“ProgrammingtheDualPLL.”
Completing Data Transmissions
Aftersending the nal dataword,the host sendsa
Stopindicatortomarktheendofdatatransmission.
A Stopisindicatedbyalow-to-hightransitionofthe
DATA signal while the CLOCK signal is held high.
AfterreceivingtheStopindicator,thedualPLLceases
to send further acknowledgements and begins to
monitor the CLOCK and DATA signals for the next
Startindicator.
Note: The Stop indicator does not directly control when
the programming data is latched or takes effect; the
data takes effect immediately following the receipt of
each three-word block of data, which represents a
complete 24-bit divider register.
Resending Data
If,forsomereason,thedatatransmissionfailsoris
interrupted,andthedualPLLfailstosendanaddress
wordordatawordacknowledgementtothehost,the
hostcanresendthedata.Toresenddata,anewStart
indicatorandaddresswordmustbesentpriortoany
datawords.
Programming The Dual PLL
Each synthesizer in the dual PLL contains
programmable Reference and Main dividers, which
allowawiderangeofoutputfrequencies.The24-bit
registersthatcontrolthedividersandotherfunctions
DATA
CLOCK
Stop
Indicator:
DATA
CLOCK
Start
Indicator:
Figure 21: Transmission Indicators
ThedualPLLmonitorstheCLOCKandDATAsignals
foraStartindicationfromthehost.AStart is indicated
bya high-to-low transitionofthe DATAsignalwhile
theCLOCKsignalishigh.Immediatelyfollowingthe
Startindicator,thehostsendsan8-bitaddressword
tothedualPLL.The8-bitwordrequiredtoaddress
thedualPLLisprogrammableviaaDCvoltagelevel
applied to the address select pin. For example, a
voltageof4V<AS<5VcorrespondstoavalueofC6h,
or11000110b.(TheMSBissentrst,LSBlast.)The
AddressSelectpin(10)decodesananalogvoltage
inputintotwodigitallogicoutputbitsAS1andAS2.The