Help understanding 2 lf commands

asper · 2015-01-09 20:18:18

lf cmdread
Usage:
<off period> <'0' period> <'1' period> <command> ['h'] -- Modulate LF reader field to send command before read (all periods in microseconds) (option 'h' for 134)

lf snoop
Usage:
['l'|'h'|<divisor>] [trigger threshold]-- Snoop LF (l:125khz, h:134khz)

I need an extensive description of those 2 commands to improve/add them in the GUI. Can someone please help me understanding each single parameter ? Examples ?

<off period> = ?
<'0' period> = ?
<'1' period> = ?
<command> = ?

<divisor> = ?
[trigger threshold] = ?

iceman · 2015-01-09 20:31:38

lf snoop:

divisor, if you want a custom low freq (Kilo hertz) to snoop you can manually set it.
Some sample values:
divisor = 88 ( 134 Khz )
divisor = 95 ( 125 Khz )

The divisor goes up, the Khz goes down.

https://github.com/Proxmark/proxmark3/b … fops.c#L73

iceman · 2015-01-09 20:33:02

Trigger threshold = don't collect the signal data if it is below this threshold..

asper · 2015-01-09 20:56:30

Thank you Ice !

Is the divisor explanation valid for all lf commands ? Is a range value between 19 and 255 valid for that parameter ?

iceman · 2015-01-09 21:07:38

the divisor should be the same for all LF commands which uses it. (only one place in the arm-src)

Remember that your antenna is tuned for a certain Khz...

asper · 2015-01-09 21:11:54

Thanks! Can you write a full command example using [trigger treshold] parameter ?

I am waiting for explanation of "lf cmdread" params:
<off period> = ?
<'0' period> = ?
<'1' period> = ?
<command> = ?

Last edited by asper (2015-01-09 21:12:04)

iceman · 2015-01-09 21:17:44

  sample:   lf snoop l
                 lf snoop l 200
                 lf snoop 95  
                 lf snoop 95 200

iceman · 2015-01-09 21:22:00

lf cmdread =

sends a command before reading.

<off period> = sleeping gap after sending and before reading.
<0 period> = what length in microsec denotes a "0"
<1 period> = what length in mirosec denotes a "1"

Defaults to 125Kz, option "H" = is for 134Khz
hrm, but where does it take it's input for the command to send?

asper · 2015-01-09 21:33:48

sample: lf snoop l
lf snoop l 200 --> snoop at 125KHz with treshold = 200
lf snoop 95 --> snoop at 125KHz no treshold
lf snoop 95 200 --> snoop at 125KHz with treshold = 200

Is this correct ?

The <command> seems to be a parameter... isn't it ?

iceman · 2015-01-09 21:57:49

problem with the command parameter, is that is only handled as a string.. I don't know if it is supposed to be a binary / hex / decimal string... like: "ff" or "1001001" or "129344"

iceman · 2015-01-09 22:00:05

aha, it's supposed to be a binary inputed string..

Sample:
lf cmdread 40 23 48 1001001
lf cmdread 40 23 48 h 1001001

iceman · 2015-01-09 22:03:17

Where
40 microsec sleeping gap before reading.
23 length of zero in micsec
48 length of one in micsec
1001001 command to send.

In LF it's antenna is power on for x micsec == 0 for y micsec == 1...

asper · 2015-01-09 22:04:51

how many bits for the <command> ?

iceman · 2015-01-09 22:13:28

No limit implemented in code, limited by UsbPacketSize of 512bytes.. So I suggest you write Max 200-300 chars

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Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

#4 2015-01-09 20:56:30

Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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Re: Help understanding 2 lf commands

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