LTC6804-1/LTC6804-2
44
680412fc
For more information www.linear.com/LTC6804-1
operaTion
DATA LINK LAYER
All Data transfers on LTC6804 occur in byte groups.
Every byte consists of 8 bits. Bytes are transferred with
the most significant bit (MSB) first. CSB must remain low
for the entire duration of a command sequence, including
between a command byte and subsequent data. On a write
command, data is latched in on the rising edge of CSB.
NETWORK LAYER
Packet Error Code
The packet error code (PEC) is a 15-bit cyclic redundancy
check (CRC) value calculated for all of the bits in a reg
-
ister group in the order they are passed, using the initial
PEC seed value of 000000000010000 and the following
characteristic polynomial
:
x15 + x14 + x10 + x8 + x7 +
x4 + x3 + 1. To calculate the 15-bit PEC value, a simple
procedure can be established:
1. Initialize the PEC to 000000000010000 (PEC is a 15-bit
register group)
2. For each bit DIN coming into the PEC register group,
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 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 the data is shifted. The final
PEC (16 bits) is the 15-bit value in the PEC register with
a 0 bit appended to its LSB
Figure 22 illustrates the algorithm described above. An
example to calculate the PEC for a 16-bit word (0x0001)
is listed in Table 24. The PEC for 0x0001 is computed as
0x3D6E after stuffing a 0 bit at the LSB. For longer data
streams, the PEC is valid at the end of the last bit of data
sent to the PEC register.
Figure 22. 15-Bit PEC Computation Circuit
DIN
I/P
O/P I/P
XOR GATE
X
012345678914 10111213
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