NXP Semiconductors MPC5644A, Reference Manual, Page: 1219 / 1735

Decimation Filter
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 1219
• The leftmost block, named Head. receives the raw data to be filtered from the PSI master block (or
from the device slave-bus interface in standalone/PSI output modes). The head type is configured
using CASCD[1:0] = 01 in the configuration register DECFILTER_MCR.
• The rightmost block, named Tail, is the last filter block in the chain. It sends the output result back
to the PSI master block (or to the device slave-bus interface in standalone/PSI input modes). This
type of cascaded block is configured using CASCD[1:0] = 10.
• The blocks in between, named Middle, do not exchange data (receive / transmit) with the PSI
master, only with other decimation filter blocks. This type of block is configured by setting
CASCD[1:0] = 11. Middle blocks are optional in a cascaded combo: two blocks, one Head block
feeding a Tail one, can be used in cascade.
NOTE
The values passed between cascaded blocks can be monitored using
Enhanced Debug Monitor (see
Section 26.5.14, Enhanced debug monitor
description ”).
• Each decimation filter block has one cascade-in and one cascade-out ports, besides the PSI
connections used in normal mode. The format of the cascade bus is described in
Section 26.5.16.2,
Cascade Mode Data/Control Bus description ”. The arrows show how they are physically
connected. The bold arrows show the connections used in cascade mode.
• The block configurations as Head, Tail or Middle must respect their physical connections such that
all the following apply:
— a Head block feeds a Middle or Tail one
— a Middle block feeds another Middle block or a Tail one
— Tail feeds no other block, and Head is fed by no other block.
• As a consequence of the conditions above, there must be one and only one Head block and one and
only one Tail block in a cascade combo.
• A group of physically chained blocks can form more than one cascade combo. For instance,
Figure 26-21 shows the same physical chain, but now with blocks 1 and 2 configured as Head and
Tail, respectively, forming one combo. The remaining blocks form another combo starting with
block 3 (Head), and ending with block N (Tail). Note that the chain-in inputs of blocks from block
3 on are used to carry output data from the first cascaded combo (Tail block 2) to the PSI master
block.
• Blocks not used in a cascaded chain can be used normally, isolated (DEFILTER_MCR field
CASCD[1:0] = 00), as exemplified in
Figure 26-22 .
• The optional connection show from block N to block 1 in Figure 26-20 allows block N to be
configured as Head or Middle, feeding block 1 configured as Middle or Tail, yielding more
flexibility, as in the last example of
Figure 26-22 .