RFHCS362AF datasheet(23/60 Pages) MICROCHIP

23 / 60 page

Preliminary

DS41189A-page 23

rfHCS362G/362F

TABLE 4-3:

CONFIG_1

4.5.5

GUARD

The Guard time between code words can be set to 0

ms, 6.4 ms, 25.6 ms and 76.8 ms. If during a series of

code words, the output changes from Hopping Code to

Seed the Guard time will increase by 3 x TE.

4.5.6

TIMOUT[0..1]

The transmission time-out can be set to 0.8 s, 3.2 s,

25.6 s or no time-out. After the time-out period, the

encoder will stop transmission and enter a low power

Shutdown mode.

4.5.7

DISC[0..9]

The discrimination bits are used to validate the

decrypted code word. The discrimination value is typi-

cally programmed with the 10 Least Significant bits of

the serial number or a fixed value.

4.5.8

OVR[0..1]

The

automatically

incrementing

synchronization

counter is at the core of generating the varying code.

Since the counter is limited to 16 bits, it overflows after

65536 increments, after which the code hopping

sequence repeats. In practice, this allows 20+ opera-

tions per day for ten years before repeating the

sequence. In addition, two overflow bits allow the

sequence to be extended further. The feature is

enabled by setting to logical “1” the two overflow bits

OVL0 and OVL1. The overflow bits form part of the

encrypted transmission, and therefore can be exam-

ined by receiver firmware. Table 4-4 shows how the

overflow bits act when they are set to one during initial

device configuration.

TABLE 4-4:

As can be seen from the table, the counter is effectively

extended by one bit, that is OVL0. In addition, OVL1

provides indication of the second counter overflow.

After the second overflow, OVL0 and OVL1 remain

zero, providing permanent evidence of the first and

second overflow events.

Bit

Address

Field

Description

Values

DISC_0

Discrimination bits

DISC

[9:0]

DISC_1

DISC_2

...

DISC_8

DISC_9

OVR_0

Overflow

OVR

[1:0]

OVR_1

XSER

Extended Serial Number

- Disable

- Enable

SEEDC

Seed Control

= Seed transmission on:

S[3210]

= 0001 (delay 1.6 s)

S[3210]

= 0101 (immediate)

= Seed transmission on:

S[3210]

= 0011 (delay 3.2 s)

S[3210]

= 1001 (immediate)

SEED_0

Seed options

- No Seed

- Limited Seed (Permanent and Delayed)

- Permanent and Delayed Seed

- Permanent Seed only

SEED_1

Sync. Counter

OVL0

OVL1

No overflow

0-FFFFH

First overflow

2nd 0-FFFFH

Second overflow

Third 0-FFFFH

Subsequent overflows

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