simulink arduino oscilloscope ,how i can get correct freuency ?

HI 

I AM TRYING TO BUILED OSCILLOSCOPE USING arduino AND simulink

i have a problem with the ferquency ,

when i give a 1Khz sine wave i got a 1.300 Khz sinwave if i give 2Khz i got about 2.600 Khz , this mean the frequency some how changes to 300hz higher for 1Khz and doubled for 2Khz frequeny

i am using arduino mega 2560 .. 1Khz 4v peak to peak sinwave carried on 2v dc.

how i can get correct freuency ?

[Ameer Hamza]

Can you show us your simulink model?

[rabei shwehdi]

[Ameer Hamza]

How do you measure the frequency in Simulink? Using scope blocks? What is the time-step of the Simulink model? Are you connecting to Arduino in external mode?

[rabei shwehdi]

hi

yes i am working in external mode

sample time .01

measuring frequency using socpe block