Enhanced Queued Analog-to-Digital Converter (eQADC)MPC5566 Microcontroller Reference Manual, Rev. 219-78 Freescale SemiconductorThe NCF flag is used to indicate command sequence non-coherency. When the NCFn flag is asserted, itindicates that the command sequence being transferred through CFIFOn became non-coherent. The NCFflag 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 aCFIFO to a buffer, it cannot successively send all the other commands of the sequence before any of thefollowing conditions are true:• The CFIFO through which commands are being transferred is pre-empted by a higher priorityCFIFO which sends commands to the same ADC. The NCF flag becomes asserted immediatelyafter the first command transfer from the pre-empting CFIFO, that is the higher priority CFIFO, tothe ADC in use is completed. Refer to Figure 19-43.• The external command buffer in use becomes empty. (Only the fullness of external buffers ismonitored 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 usedifferent external command buffers and the higher priority CFIFO bars the lower priority one fromsending new commands to its buffer—see Figure 19-44. An external command buffer isconsidered empty when the corresponding BUSY field in the last result message received fromexternal device is encoded as “Send available commands - buffer is empty”. Refer to Section ,“Result Message Format for External Device Operation.” The NCF flag becomes assertedimmediately after the eQADC detects that the external buffer in use becomes empty.NOTEAfter the transfer of a command sequence to an external command bufferstarts, the eQADC ignores, for non-coherency detection purposes, theBUSY fields captured at the end of the first serial transmission. Thereafter,all BUSY fields captured at the end of consecutive serial transmissions areused to check the fullness of that external command buffer. This is donebecause the eQADC only updates its external ADC command buffer statusrecord when it receives a serial message, resulting that the record kept bythe eQADC is always outdated by, at least, the length of one serialtransmission. This prevents a CFIFO from immediately becomingnon-coherent when it starts transferring commands to an empty externalcommand buffer. Refer to Figure 19-42 for an example.Figure 19-42. External Command Buffer Status Detection at Command Sequence Transfer StartSDSNull MessageSerial DataTransmitted1) 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 toAssumptions:complete two serial transmissions.Command 3Command 2Command 1(a) (b) (c)Transfer of CommandSequence StartsExternal Buffer Status Startsto be Monitored Here
