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 Section 19.4.5.3,
“Time Stamp Feature.”
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.
0Write
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 19-25.
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 Reserved for customer use.
1
0b1011–0b1111 Reserved
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