MCP3550/1/3 - Microchip

MCP3550/1/35.3 Single Conversion ModeIf a rising edge of Chip Select (CS) occurs during t CONV ,a subsequent conversion will not take place and thedevice will enter low-power Shutdown mode aftert CONV completes. This is referred to as SingleConversion mode. This operation is demonstrated inFigure 5-2. Note that a falling edge of CS during thesame conversion that detected a rising edge, as inFigure 5-2, will not initiate a new conversion. The datamust be read during sleep mode, with CSN low, and willbe lost as soon as the part enters in shutdown mode(with a rising edge of CSN). After the final data bit hasbeen clocked out on the 25th clock, the SDO/RDY pinwill go active-high.5.3.1 READY FUNCTION OF SDO/RDYPIN, SINGLE CONVERSION MODEAt every falling edge of CS during the internalconversion, the state of the internal conversion islatched on the SDO/RDY pin to give ready or busyinformation. A High state means the device is currentlyperforming an internal conversion and data cannot beclocked out. A Low state means the device has finishedits conversion and the data is ready for retrieval on thefalling edge of SCK. This operation is demonstrated inFigure 5-4. Note that the device has been put intoSingle Conversion mode with the first rising edge ofCS.Note:CSInt. OscThe Ready state is latched on each fallingedge of CS and will not dynamicallyupdate if CS is held low. CS must betoggled high through low.t CONV5.4 Continuous Conversion ModeIf no rising edge of CS occurs during any givenconversion per Figure 5-3, a subsequent conversionwill take place and the contents of the previous conversionwill be overwritten. This operation is demonstratedin Figure 5-5. Once conversion output data has startedto be clocked out, the output buffer is not refreshed untilall 24 bits have been clocked. A complete read mustoccur in order to read the next conversion in this mode.The subsequent conversion data to be read will then bethe most recent conversion. The conversion time isfixed and cannot be shortened by the rising edge of CS.This rising edge will place the part in Shutdown modeand all conversion data will be lost.The transfer of data from the SINC filter to the outputbuffer is demonstrated in Figure 5-5. If the previousconversion data is not clocked out of the device, it willbe lost and replaced by the new conversion. When thedevice is in Continuous Conversion mode, the mostrecent conversion data is always present at the outputregister for data retrieval.CSInt. Osct CONVSCK & SDO/RDYt CONVtCONVA B CConversion B data is clockedout of the device here.FIGURE 5-5: Most Current ContinuousConversion Mode Data.If a conversion is in process, it cannot be terminatedwith the rising edge of CS. SDO/RDY must firsttransition to a Low state, which will indicate the end ofconversion.SDO/RDYFIGURE 5-4:Conversion Mode.Hi-ZRDY Functionality in Single© 2009 Microchip Technology Inc. DS21950E-page 23