CS5531/32/33/34 - Eshop-Rychle.cz

CS5531/32/33/34Using the single conversion mode, an 8-bit commandword can be written into the serial port. Thecommand includes pointer bits which ‘point’ to a16-bit command in one of the Channel Setup Registerswhich is to be executed. The 16-bit Setupscan be programmed to perform a conversion on anyof the input channels of the converter. More thanone of the 16-bit Setups can be used for the sameanalog input channel. This allows the user to converton the same signal with either a different conversionspeed, a different gain range, or any of theother options available in the channel setup registers.Alternately, the user can set up the registers toperform different conversion conditions on each ofthe input channels.The ADCs also include continuous conversion capability.The ADCs can be instructed to continuouslyconvert, referencing one 16-bit commandSetup. In the continuous conversions mode, theconversion data words are loaded into a shift register.The converter issues a flag on the SDO pinwhen a conversion cycle is completed so the usercan read the register, if need be. See the section onPerforming Conversions for more details.The following pages document how to initialize theconverter, perform offset and gain calibrations, andhow to configure the converter for the various conversionmodes. Each of the bits of the configurationregister and of the Channel Setup Registers is described.A list of examples follows the descriptionsection. Also the Command Register Quick Referencecan be used to decode all valid commands (thefirst 8-bits into the serial port).2.2.1. System InitializationThe CS5531/32/33/34 provide no power-on-resetfunction. To initialize the ADCs, the user must performa software reset by resetting the ADC’s serialport with the Serial Port Initialization sequence.This sequence resets the serial port to the commandmode and is accomplished by transmitting at least15 SYNC1 command bytes (0xFF hexadecimal),followed by one SYNC0 command (0xFE hexadecimal).Note that this sequence can be initiated atanytime to reinitialize the serial port. To completethe system initialization sequence, the user mustalso perform a system reset sequence which is asfollows: Write a logic 1 into the RS bit of the configurationregister. This will reset the calibrationregisters and other logic (but not the serial port). Avalid reset will set the RV bit in the configurationregister to a logic 1. After writing the RS bit to alogic 1, wait 20 microseconds, then write the RS bitback to logic 0. While this involves writing an entireword into the configuration register, the RV bitis a read only bit, therefore a write to the configurationregister will not overwrite the RV bit. Afterclearing the RS bit back to logic 0, read the configurationregister to check the state of the RV bit asthis indicates that a valid reset occurred. Readingthe configuration register clears the RV bit back tologic 0.Completing the reset cycle initializes the on-chipregisters to the following states:Note:Configuration Register:Offset Registers:Gain Registers:Channel Setup Registers:00000000(H)00000000(H)01000000(H)00000000(H)Previous datasheets stated that the RS bitwould clear itself back to logic 0 and thereforethe user was not required to write the RS bitback to logic 0. The current data sheetinstruction that requires the user to write intothe configuration register to clear the RS bithas been added to insure that the RS bit iscleared. Characterization across multiple lotsof silicon has indicated some chips do notautomatically reset the RS bit to logic 0 in theconfiguration register, although the resetfunction is completed. This occurs only onsmall number of chips when the VA- supply isnegative with respect to DGND. This has notcaused an operational issue for customersbecause their start-up sequence includeswritingaword(withRS=0)intotheconfiguration register after performing areset. The change in the reset sequence toDS289PP5 17