Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 19-57
Result Message Format for External Device Operation
Data is returned from the ADCs in the form of result messages. A result message is composed of an RFIFO
header and an ADC result. The FIFO control unit decodes the information contained in the RFIFO header
and sends the contents of the ADC result to the appropriate RFIFO. Only data stored on the
ADC_RESULT field is stored in the RFIFOs result queues. The ADC result of any received message with
a null data message tag is ignored. The format of a result message returned from the external device is
shown in Figure 19-32. It is 26 bits long, and is composed of a MESSAGE_TAG field, information about
the status of the buffers (BUSY fields), and result data. The BUSY fields are needed to inform the eQADC
about when it is appropriate to transfer commands to the external command buffers.
0123456789101112131415
Reserved MESSAGE_TAG BUSY1 BUSY0
RFIFO Header
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
ADC_RESULT
ADC Result
Figure 19-32. Result Message Format for External Device Operation
Table 19-41. Result Message Format for External Device Operation
Field Description
6–7 Reserved.
8–11
MESSAGE
_TAG[0:3]
MESSAGE_TAG Field. Refer to Section , “Conversion Command Message Format for On-Chip ADC Operation.”
12–15
BUSYn
[0:1]
BUSY status. The BUSY fields indicate if the external device can receive more commands. Ta bl e 1 9 -42 shows
how these two bits are encoded. When an external device cannot accept any more new commands, it must set
BUSYn to a value indicating “Do not send commands” in the returning message. The BUSY fields of values 0b10
and 0b10 can be freely encoded by the external device to allow visibility of the status of the external command
buffers for debug. As an example, they could indicate the number of entries in an external command buffer.
16–31
ADC_
RESULT
[0:15]
ADC RESULT Field. The result data received from the external device or on-chip ADC can be any value produced
by the external device, such as the result of a conversion command, data requested via a read configuration
command, or a time stamp value. The ADC_RESULT of any incoming message with a null message tag is
ignored. When the MESSAGE_TAG is for an RFIFO, the eQADC extracts the 16-bit ADC_RESULT from the raw
message and stores it into the appropriate RFIFO.
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