Freescale Semiconductor MPC5565, Reference Manual

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Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor 18-79
The NCF flag is used to indicate command sequence non-coherency. When the NCF n flag is asserted, it
indicates that the command sequence being transferred through CFIFO n became non-coherent. The NCF
flag only becomes asserted for CFIFOs in a TRIGGERED state.
A command sequence is non-coherent when, after transferring the first command of a sequence from a
CFIFO to a buffer, it cannot successively send all the other commands of the sequence before any of the
following conditions are true:
• The CFIFO through which commands are being transferred is pre-empted by a higher priority
CFIFO which sends commands to the same ADC. The NCF flag becomes asserted immediately
after the first command transfer from the pre-empting CFIFO, that is the higher priority CFIFO, to
the ADC in use is completed. Refer to
Figure 18-43 .
• The external command buffer in use becomes empty. (Only the fullness of external buffers is
monitored because the fill rate for internal ADC buffers is many times faster than the drain rate,
and each has a dedicated priority engine.)
This case happens when different CFIFOs attempt to use
different external command buffers and the higher priority CFIFO bars the lower priority one from
sending new commands to its buffer—see
Figure 18-44 . An external command buffer is
considered empty when the corresponding BUSY field in the last result message received from
external device is encoded as “Send available commands - buffer is empty”. Refer to
Section ,
“Result Message Format for External Device Operation .” The NCF flag becomes asserted
immediately after the eQADC detects that the external buffer in use becomes empty.
NOTE
After the transfer of a command sequence to an external command buffer
starts, the eQADC ignores, for non-coherency detection purposes, the
BUSY fields captured at the end of the first serial transmission. Thereafter,
all BUSY fields captured at the end of consecutive serial transmissions are
used to check the fullness of that external command buffer. This is done
because the eQADC only updates its external ADC command buffer status
record when it receives a serial message, resulting that the record kept by
the eQADC is always outdated by, at least, the length of one serial
transmission. This prevents a CFIFO from immediately becoming
non-coherent when it starts transferring commands to an empty external
command buffer. Refer to
Figure 18-42 for an example.
Figure 18-42. External Command Buffer Status Detection at Command Sequence Transfer Start
SDS
Null Message
Serial Data
Transmitted
1) The CFIFO starts sending commands to an external command buffer when triggered.
2) Execution of a command on the external device takes longer than the time to Assumptions:
complete three serial transmissions.
Command 3 Command 2 Command 1
(a) (b) (c)
Transfer of Command
Sequence Starts External Buffer Status Starts
to be Monitored Here