RFHCS362F datasheet(15/54 Pages) MICROCHIP

15 / 54 page

DS41189B-page 15

rfHCS362G/362F

3.1.4.2

Button Queue Information (QUEUE)

The queue bits indicate a button combination was

pressed again within 2 s after releasing the previous

activation. Queuing or repeated pressing of the same

buttons (or button combination) is detected by the

rfHCS362 button debouncing circuitry.

The Queue bits are added as the last two bits of the

standard code word. The queue bits are a 2-bit counter

that does not wrap. The counter value starts at ‘00b’

and is incremented if a button is pushed within 2 s of

the previous button press. The current code word is ter-

minated when the buttons are queued. This allows

additional functionality for repeated button presses.

The button inputs are sampled every 6.4 ms during this

2 s period.

- first activation

- second activation

- third activation

- from fourth activation on

3.1.4.3

Time BITS

The time bits (Figure 3-5) indicate the duration that the

inputs were activated:

- immediate

- after 0.8 s

- after 1.6 s

- after 2.4 s

The TIME bits are incremented every 0.8 s and will not

wrap once it reaches ‘11’.

Time information is alternative to the CRC bits availabil-

ity and is selected by the CTSEL configuration bit.

FIGURE 3-5:

TIME BITS OPERATION

3.1.4.4

Cyclic Redundancy Check (CRC)

The CRC bits are calculated on the 65 previously trans-

mitted bits. The decoder can use the CRC bits to check

the data integrity before processing starts. The CRC

can detect all single bit errors and 66% of double bit

errors. The CRC is computed as follows:

EQUATION 3-1:

CRC Calculation

and

with

and Din the nth transmission bit 0 ≤n ≤64

TTD

Time

DATA

= One Code Word

Time bits = 00

Time bits set internally to 01

Time bits actually output

Time bits set internally to 10

Time bits actually output

0 s

0.8 s

1.6 s

2.4 s

S[3210]

CRC 1

[]n1

CRC 0

[]n Din

⊕

CRC 0

[]n1

CRC 0

[]n Din

⊕

()

CRC 1

[]n

⊕

CRC 1 0

[]0

Warning: The CRC may be wrong when the battery

voltage is near the selected VLOW trip point.

This may happen because VLOW is sam-

pled twice each transmission, once for the

CRC calculation and once when VLOW is

transmitted. VDD tends to move slightly dur-

ing a transmission which could lead to a dif-

ferent value for VLOW being used for the

CRC calculation and the transmission.

Work around: If the CRC is incorrect,

recalculate for the opposite value of VLOW.

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