Enhanced Queued Analog-to-Digital Converter (eQADC)MPC5566 Microcontroller Reference Manual, Rev. 2Freescale Semiconductor 19-53ADC Result Format for On-Chip ADC OperationWhen the FIFO control unit receives a return data message, it decodes the MESSAGE_TAG field andstores the 16-bit data into the appropriate RFIFO. This section describes the ADC result portion of theresult message returned by the on-chip ADCs.The 16-bit data stored in the RFIFOs can be the following:• Data read from an ADC register with a read configuration command. In this case, the stored 16-bitdata corresponds to the contents of the ADC register that was read.• A time stamp. In this case, the stored 16-bit data is the value of the time base counter latched whenthe eQADC detects the end of the analog input voltage sampling. For details see Section 19.4.5.3,“Time Stamp Feature.”• A conversion result. In this case, the stored 16-bit data contains a right justified 14-bit result data.The conversion result can be calibrated or not depending on the status of CAL bit in the commandthat requested the conversion. When the CAL bit is negated, this 14-bit data is obtained byexecuting a 2-bit left-shift on the 12-bit data received from the ADC. When the CAL bit is asserted,8–11MESSAGE_TAG[0:3]MESSAGE_TAG field. Allows the eQADC to separate returning results into different RFIFOs. When the eQADCtransfers a command, the MESSAGE_TAG is included as part of the command. Eventually the externaldevice/on-chip ADC returns the result with the same MESSAGE_TAG. The eQADC separates incomingmessages into different RFIFOs by decoding the MESSAGE_TAG of the incoming data.12–23 Reserved.24–31ADC_REG_ADDRESS[0:7]ADC register address. Identifies to which ADC register the read or write is performed. Only use 16-bit (halfword)addresses. Refer to Table 19-25. Refer to Table 19-25.Table 19-36. On-Chip ADC Field Descriptions: Read Configuration (continued)Field DescriptionMESSAGE_TAG[0:3] MESSAGE_TAG Meaning0b0000 Result is sent to RFIFO 00b0001 Result is sent to RFIFO 10b0010 Result is sent to RFIFO 20b0011 Result is sent to RFIFO 30b0100 Result is sent to RFIFO 40b0101 Result is sent to RFIFO 50b0110–0b0111 Reserved0b1000 Null message received0b1001 Reserved for customer use. 11 These messages are treated as null messages. Therefore, they must obey theformat for incoming null messages and return valid BUSY0/1 fields. Refer toSection , “Null Message Format for External Device Operation.”0b1010 Reserved for customer use. 10b1011–0b1111 Reserved
