Decimation Filter
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1201
9–10
M_CTRL[1:0]
Decimation Filter mode control bits.
describes the M_CTRL[1:0] field functions. This
field is used for control of the Decimation Filter.
11
Reserved, should be cleared.
12–15
INP_TAG[3:0]
Decimation filter input tag bits. The INP_TAG[3:0] field indicates the destination associated with
the INPBUFF[15:0] sample. This value is stored by the Decimation Filter and used to address
the destination register when a decimated sample is available to be read by the master block.
Since several input data samples can be received before a decimated result is generated, the
INP_TAG[3:0] used for the decimated sample corresponds to the latest INP_TAG[3:0] received.
Therefore it is expected that the tag field be constant during the decimation process.
12–15
OUT_TAG[3:0]
Decimation filter output tag bits. The OUT_TAG[3:0] bit field is used to address the appropriate
destination register in the master block for the accompanying OUTBUF[15:0] data. When this
value is updated, it is a copy of the INP_TAG[3:0] value that was received with the last processed
input data.
When an eQADC is the PSI master block, this is used to address the appropriate RFIFO in the
eQADC block.
16–31
INP_BUFF[15:0]
Input Buffer Data. The INP_BUFF[15:0] bit field is the data input from the master block. The input
register can be written with this data when ISEL = 0. This data can be timestamp information that
is not processed by the filter, or sample data that is processed by the digital filter. In this case,
the information is a signed signal in two’s complement format.
16–31
OUT_BUFF[15:0]
Output Buffer Data. The OUT_BUFF[15:0] bit field corresponds to the data result of the
decimation filter that has been processed to the master block. This data can be timestamp
information or a digital filter result. In this case, the information is a signed signal in two’s
complement format.
Table 26-28. DECFILTER_IOB Register Field Descriptions (continued)
Field
Description
Table 26-29. M_CTRL[1:0] – Decimation filter control functions
M_CTRL[1:0]
Description
00
PREFILL — A prefill indicates to the Decimation Filter to accept
INP_BUFF[15:0] as valid data but no decimated samples are generated out of
these master samples. The prefill function is used to initialize and stabilize the
Decimation Filter without generating decimated samples.
01
CONVERSION RESULT — A conversion result indicates that the
INP_BUFF[15:0] field is data to be treated as valid sample data and it is
considered for decimation counting and output buffer update.
10
TIMESTAMP — A timestamp indicates that the INP_BUFF[15:0] field has data
that bypasses the flow in the decimation filter logic, returning back to the
master block without any modification when:
• the previous accompanying data is not for prefill, and
• when the previous accompanying input data is generating decimated filter
output.
Also, bit M_FLUSH is always 0 for timestamp data type.
11
Reserved
Summary of Contents for MPC5644A
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