Freescale Semiconductor MPC5553, Справочное руководство

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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
19-76 Freescale Semiconductor
Figure 19-41. Command Sequence Examples
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. See
Figure 19-43 .
• 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
The eQADC would check for non-coherency of seven command
sequences, all containing a single command, but NCF would never get set.
CF n _ADCa_CMD n – Command n in CFIFO n bound for ADCa (ADC3
and ADC4 are external devices associated with external command buffers
2 and 3).
Assuming that these commands are transferred by a CFIFO configured for
edge trigger mode and the command transfers are never interrupted, the
eQADC would check for non-coherency of two command sequences: one
formed by commands 0, 1, 2, 3, and the other by commands 4, 5, 6.
Assuming that command transfers from the CFIFO are never interrupted,
the eQADC would check for non-coherency of three command sequences.
The first being formed by commands 0, 1, 2, the second by commands 3,
4 and the third by commands 5, 6. Note that even when the commands of
this queue are transferred through a CFIFO in continuous-scan mode, the
first three commands and the last two commands of this command queue
would still constitute two distinct command sequences, although they are
all bound for the same ADC, because an asserted EOQ ends a command
sequence.
User Command Queue with
Two Command Sequences
CF5_ADC1_CM6(EOQ=1) 7
CF5_ADC1_CM5 6
CF5_ADC1_CM4 5
CF5_ADC1_CM3(Pause=1) 4
CF5_ADC1_CM2 3
CF5_ADC1_CM1 2
CF5_ADC1_CM0 1
Example 1
User Command Queue with
Three Command Sequences
CF5_ADC1_CM6(EOQ=1) 7
CF5_ADC1_CM5 6
CF5_ADC0_CM4 5
CF5_ADC0_CM3 4
CF5_ADC1_CM2 3
CF5_ADC1_CM1 2
CF5_ADC1_CM0 1
Example 2
User Command Queue with a
Seven Command Sequence
CF5_ADC1_CM6(EOQ=1) 7
CF5_ADC2_CM5 6
CF5_ADC0_CM4 5
CF5_ADC1_CM3 4
CF5_ADC3_CM2 3
CF5_ADC2_CM1 2
CF5_ADC1_CM0 1
Example 3