# measuring freq of serial bits....

#### Polgi-Wan

Joined Sep 26, 2005
11
hi guys,

for example you have a serial data with 000111000111000 and bit-rate at 10ns.... how will I be able to measure the frequency of this one? pls guide me through the steps....

thanks!

#### Papabravo

Joined Feb 24, 2006
18,816
Are all of the bits the same length, or does the encoding scheme use more time for a zero or vice versa. If all the bits are the same length then you measure the time occupied by a group of bits and divide by the number of bits.

There will be at least two types of errors present. A drift error which is additive, due to error in the clock based on the crystal. The other error will be random and depend on things like temperature, power supply voltage and other factors.

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

The bit rate may be considered as the wavelength of the signal. You take the reciprocal of it to get the frequency. For 10 ns, it will be 100 MHz.

#### Polgi-Wan

Joined Sep 26, 2005
11
Papabravo said:
Are all of the bits the same length, or does the encoding scheme use more time for a zero or vice versa. If all the bits are the same length then you measure the time occupied by a group of bits and divide by the number of bits.

There will be at least two types of errors present. A drift error which is additive, due to error in the clock based on the crystal. The other error will be random and depend on things like temperature, power supply voltage and other factors.
thanks! yes, same length. just curious on why should i divide the total time by number of bits. since my example was 000111000111000.... should'nt I be getting the -000111- period? instead of the entire set? regards.

#### Polgi-Wan

Joined Sep 26, 2005
11
beenthere said:
Hi,

The bit rate may be considered as the wavelength of the signal. You take the reciprocal of it to get the frequency. For 10 ns, it will be 100 MHz.
i'm kinda new to data communications. when it is mentioned as 10ns bit-rate is it referring to 10ns per bit or 10ns for the entire bits (one-shot)?

thanks!

#### pebe

Joined Oct 11, 2004
626
Polgi-Wan said:
thanks! yes, same length. just curious on why should i divide the total time by number of bits. since my example was 000111000111000.... should'nt I be getting the -000111- period? instead of the entire set? regards.
Yes, each cycle consists of 6 bits, so the frequency is 16.67MHz

#### Dave

Joined Nov 17, 2003
6,969
Polgi-Wan said:
i'm kinda new to data communications. when it is mentioned as 10ns bit-rate is it referring to 10ns per bit or 10ns for the entire bits (one-shot)?

thanks!
There is a certain level of ambitguity in what has gone previous, let me clarify a few things. In data communications the bit rate refers to the number of bits transmitted in a specific period of time, for example x-bits per second would refer to the bit rate. When it says 10ns bit rate, it should actually specify explicitly whether it is 10ns per-bit or 10 ns per bit-sequence for it to have any meaning.

Dave

#### Papabravo

Joined Feb 24, 2006
18,816
I appologize for my misunderstanding. I interpreted your question in a way that suggested that you knew the theoretical bit rate (10 ns/bit) and were interested in measuring the actual bit rate. In that case you would want to start with the mean or average bit rate over some number of bits. Sorry for the confustion.