CC1110Fx / CC1111Fx
12.11 Random Number Generator
12.11.1 Introduction
The random number generator is a 16-bit
Linear Feedback Shift Register (LFSR) with
The random number generator has the
following features.
X16 X15 X 2
polynomial
(i.e. CRC16).
1
It uses different levels of unrolling depending
on the operation it performs. The basic version
(no unrolling) is shown below.
Generate pseudo-random bytes which
can be read by the CPU.
Calculate CRC16 of bytes that are
written to RNDH.
The random number generator is turned off
when ADCCON1.RCTRL=11.
Seeded by value written to RNDL.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
+
+
in_bit
+
Figure 40: Basic Structure of the Random Number Generator
Number Generator 12.11.2.3 CRC16
12.11.2 Random
Operation
The LFSR can also be used to calculate the
CRC value of a sequence of bytes. Writing to
The operation of the random number generator
is controlled by the ADCCON1.RCTRLbits. The
current value of the 16-bit shift register in the
LFSR can be read from the RNDH and RNDL
registers.
the RNDH register will trigger
a
CRC
calculation. The new byte is processed from
the MSB end and an 8x unrolling is used, so
that a new byte can be written to RNDH every
clock cycle.
Note that the LFSR must be properly seeded
by writing to RNDL twice, before the CRC
calculations start. Usually the seed value
should be 0x0000 or 0xFFFF. Using 0xFFFF
as seed value will give the CRC used by the
radio.
12.11.2.1 Semi Random Sequence
Generation
To
generate
pseudo-random
bytes,
ADCCON1.RCTRLshould be set to 01. This will
clock the LFSR once (13x unrolling) and the
ADCCON1.RCTRL bits will automatically be
cleared when the operation has completed.
For the following byte sequence:
0x03, 0x41, 0x42, 0x43
12.11.2.2 Seeding
The CRC will be 0xB4BC when using 0xFFFF
as seed value.
The LFSR can be seeded by writing to the
RNDL register twice. Each time the RNDL
register is written, the 8 LSB of the LFSR is
copied to the 8 MSB and the 8 LSBs are
replaced with the new data byte that was
written to RNDL.
12.11.3 Registers
The random number generator registers are
described in this section.
SWRS033H
Page 147 of 246
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