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Chapter 29 128 Kbyte Flash Module (S12XFTX128K1V1)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

1217

29.4.2.2.1

Data Compress Operation

The Flash module contains a 16-bit multiple-input signature register (MISR) to generate a 16-bit signature

based on selected Flash array data. The ﬁnal 16-bit signature, found in the FDATA registers after the data

compress operation has completed, is based on the following logic equation which is executed on every

data compression cycle during the operation:

MISR[15:0] = {MISR[14:0], ^MISR[15,4,2,1]} ^ DATA[15:0]

Eqn. 29-1

where MISR is the content of the internal signature register and DATA is the data to be compressed as

shown in Figure 29-25.

Figure 29-25. 16-Bit MISR Diagram

During the data compress operation, the following steps are executed:

1. MISR is reset to 0xFFFF.

2. Initialized DATA equal to 0xFFFF is compressed into the MISR which results in the MISR

containing 0x0001.

3. DATA equal to the selected Flash array data range is read and compressed into the MISR with

addresses incrementing.

4. DATA equal to the selected Flash array data range is read and compressed into the MISR with

addresses decrementing.

5. DATA equal to the contents of the MISR is compressed into the same MISR.

6. The contents of the MISR are written to the FDATA registers.

= Exclusive-OR

DATA[0]

DATA[1]

DATA[2]

DATA[3]

DATA[4]

DATA[5]

DATA[15]

M15

...

MISR[15:0] = Q[15:0]

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