ADBMS2950BCCSZ datasheet(23/97 Pages) AD

23 / 97 page

Data Sheet

ADBMS2950B

Rev. 0 | Page 23 of 97

For read commands, register data is received from

ADBMS2950B, followed by the DPEC. For example, when

reading CFGA, the data is received in the following order:

CFGA0, …, CFGA5, DPEC0, and DPEC1. Table 32 shows the

format for the DPEC when reading data.

Read and write commands may be interrupted at any device

boundary (multiple of 8 bytes, not counting the initial 4 CMD,

PEC bytes) to read from or write to a leading device subset of

the daisy-chain only. The command counter of the devices not

being accessed does not increment.

Command PEC

The command-packet error code (CPEC) is a 15-bit CRC value

(PEC15) calculated for all 16 bits of a command, which uses the

initial PEC value of 0b000000000010000 and the following

characteristic polynomial:

x15 + x14 + x10 + x8 + x7 + x4 + x3 + 1

To calculate the 15-bit command PEC value, a simple procedure

can be established, as follows:

1. Initialize the Command PEC to 0b000000000010000

(15-bit value).

2. For each bit DIN, set:

IN0 = DIN XOR PEC[14]

IN3 = IN0 XOR PEC[2]

IN4 = IN0 XOR PEC[3]

IN7 = IN0 XOR PEC[6]

IN8 = IN0 XOR PEC[7]

IN10 = IN0 XOR PEC[9]

IN14 = IN0 XOR PEC[13]

3. Update the 15-bit Command PEC as follows:

PEC[14] = IN14

PEC[13] = PEC[12]

PEC[12] = PEC[11]

PEC[11] = PEC[10]

PEC[10] = IN10

PEC[9] = PEC[8]

PEC[8] = IN8

PEC[7] = IN7

PEC[6] = PEC[5]

PEC[5] = PEC[4]

PEC[4] = IN4

PEC[3] = IN3

PEC[2] = PEC[1]

PEC[1] = PEC[0]

PEC[0] = IN0

4. Go back to step 2 until all 16 command bits are

shifted.

The final PEC (16 bits) is the 15-bit value in the PEC register

with a 0-bit appended to the LSB. The ADBMS2950B calculates

the command PEC for any command received and compares it

to the PEC following the command. The command is valid only

if the PEC matches. Table 30 shows the format of the command

PEC.

Table 30. Command PEC Format

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

PEC0

PEC[14]

PEC[13]

PEC[12]

PEC[11]

PEC[10]

PEC[9]

PEC[8]

PEC[7]

PEC1

PEC[6]

PEC[5]

PEC[4]

PEC[3]

PEC[2]

PEC[1]

PEC[0]

Data PEC

The data-packet error code (DPEC) is a 10-bit CRC value

calculated for data bits, which includes the command counter

bits, during a read or write commands. This data includes

(0b000000 for write commands). Data is regarded as valid only

if the data PEC matches.

The initial data PEC value is 0b0000010000 and the following

characteristic polynomial: x10 + x7 + x3 + x2 + x + 1.

To calculate the 10-bit data PEC value, a simple procedure can

be established, as follows:

1. Initialize the data PEC to 0b0000010000 (10-bit

value).

2. For each bit DIN, set:

IN0 = DIN XOR PEC[9]

IN1 = IN0 XOR PEC[0]

IN2 = IN0 XOR PEC[1]

IN3 = IN0 XOR PEC[2]

IN7 = IN0 XOR PEC[6]

3. Update the 10-bit data PEC as follows:

PEC[9] = PEC[8]

PEC[8] = PEC[7]

PEC[7] = IN7

PEC[6] = PEC[5]

PEC[5] = PEC[4]

PEC[4] = PEC[3]

PEC[3] = IN3

PEC[2] = IN2

PEC[1] = IN1

PEC[0] = IN0

4. Go back to step 2 until all the data, including six

command counter bits (0b000000 for write

commands) is shifted.

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