MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 19-47
19.4.1.2 Message Format in eQADC
This section explains the command and result message formats used for on-chip ADC operation and for
external device operation.
A command message is the pre-defined format at which command data is stored in the user command
queues. A command message has 32 bits and is composed of two parts: a CFIFO header and an ADC
command. The size of the CFIFO header is fixed to 6 bits, and it works as inputs to the FIFO control unit.
The header controls when a command queue ends, when it pauses, if commands are sent to internal or
external buffers, and if it can abort a serial data transmission. Information contained in the CFIFO header,
together with the upper bit of the ADC command, is used by the FIFO control unit to arbitrate which
triggered CFIFO will transfer the next command. ADC commands are encoded inside the least significant
26 bits of the command message.
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 to determine the RFIFO to which the ADC result should be
sent. An ADC result is always 16 bits long.
19.4.1.2.1 Message Formats for On-Chip ADC Operation
This section describes the command/result message formats used for on-chip ADC operation.
NOTE
Although this subsection describes how the command and result messages
are formatted to communicate with the on-chip ADCs, nothing prevents the
programmer from using a different format when communicating with an
external device through the serial interface. Refer to Section 19.4.1.2.2,
“Message Formats for External Device Operation.” Apart from the BN bit,
the ADC command of a command message can be formatted to
communicate to an arbitrary external device provided that the device returns
an RFIFO header in the format expected by the eQADC. When the FIFO
control unit receives return data message, it decodes the message tag field
and stores the 16-bit data into the corresponding RFIFO.
Conversion Command Message Format for On-Chip ADC Operation
Figure 19-26 describes the command message format for conversion commands when interfacing with the
on-chip ADCs. A conversion result is always returned for conversion commands and time stamp
information can be optionally requested. The lower byte of conversion commands is always set to 0 to
distinguish it from configuration commands.
0 1 23456789101112131415
EOQ PAUSE Reserved EB
(0b0)
BN CAL MESSAGE_TAG LST TSR FMT
CFIFO Header ADC Command
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
CHANNEL_NUMBER 00000000
ADC Command
Figure 19-26. Conversion Command Message Format for On-Chip ADC Operation
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