Data processing in array

[richard]

In a noisy environment you can over sample a bit to be sure of data validity, i expect the serial data from a keeloq
chip to be quite clean so a single sample point would suffice

sample @50,250,450,650,850 uS past transition to hi
where valid result is
11000 for a 1
11110 for a 0

sample var bitfail var bit


fail=0
pulsetrain:
index=67 
while index && !fail
while  !portb.0 :wend   
pauseus 50               ;50
if   !portb.0 then  fail = fail | 1
pauseus 200              ;250
if   !portb.0 then  fail = fail | 1
pauseus 200              ;450
sample=portb.0
pauseus 200               ;650
if   portb.0^sample then  fail = fail | 1
pauseus 200               ;850
if   portb.0 then  fail = fail | 1
index=index-1

code.0[index]= !sample

wend

[Ioannis]

In general the data stream on a good signal level is very clean. But when there is no RF signal, the radio module will produce a lot of noise that is converted to random pulses through the data slicer. This creates a lot of bad data and false triggers on a non rolling code systems if digital filtering is not applied. With the keeloq encryption it is safe to assume that such triggers will not happen. The probability to have 66 bits in a correct timing and also in the correct sequence, not mentioning the other safety measures of keeloq like counter etc, is really low if not zero.

When you referred to 5 sampling points I was thinking of timers etc to maintain a fixed sampling point in time...

Your code showed the application of KISS in a fine way!

Thank you for your great ideas,
Ioannis

[richard]

The probability to have 66 bits in a correct timing and also in the correct sequence, not mentioning the other safety measures of keeloq like counter etc, is really low if not zero.

i would not expect to ever receive a malformed bit from a keeloq serial stream , the data may be useless however.
single point sampling should be ok imho

[Ioannis]

Agree.

Though I have checked various implementations of RF remote controls and many have wide tolerances from the specified timings.

I am very much sure that those chips are bad copies of the original Microchip one. But are out there... If interested, I have many test of original and copy chips with the timings in excel file.

Ioannis