MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
19-53
ADC Result Format for On-Chip ADC Operation
When the FIFO control unit receives a return data message, it decodes the MESSAGE_TAG field and
stores the 16-bit data into the appropriate RFIFO. This section describes the ADC result portion of the
result 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-bit
data 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 when
the eQADC detects the end of the analog input voltage sampling. For details see
6
BN
Buffer number. Indicates which buffer the message will be stored in. Buffers 1 and 0
can either be internal or external depending on the EB bit setting.
0 Message stored in buffer 0.
1 Message stored in buffer 1.
7
R/W
Read/write. An asserted R/W bit indicates a read configuration command.
0 Write
1 Read
8–11
MESSAGE_TAG
[0:3]
MESSAGE_TAG field. Allows the eQADC to separate returning results into different
RFIFOs. When the eQADC transfers a command, the MESSAGE_TAG is included as
part of the command. Eventually the external device/on-chip ADC returns the result
with the same MESSAGE_TAG. The eQADC separates incoming messages into
different RFIFOs by decoding the MESSAGE_TAG of the incoming data.
12–23
—
Reserved.
24–31
ADC_REG_
ADDRESS
[0:7]
ADC register address. Selects a register on the ADC register set to be written or read.
Only halfword addresses can be used. See
Table 19-36. On-Chip ADC Field Descriptions: Read Configuration (Continued)
Bits
Name
Description
MESSAGE_TAG[0:3]
MESSAGE_TAG Meaning
0b0000
Result is sent to RFIFO 0
0b0001
Result is sent to RFIFO 1
0b0010
Result is sent to RFIFO 2
0b0011
Result is sent to RFIFO 3
0b0100
Result is sent to RFIFO 4
0b0101
Result is sent to RFIFO 5
0b0110–0b0111
Reserved
0b1000
Null message received
0b1001
Reserved for customer use.
1
1
These messages are treated as null messages. Therefore, they must obey the
format for incoming null messages and return valid BUSY0/1 fields. Refer to
Section , “ Null Message Format for External Device Operation
.”
0b1010
0b1011–0b1111
Reserved
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