Topic: right way to write to ultralight

hello all,
this is my first topic, i want to ask you guys i have mifare ultralight and i want to change page 3
u know that page 3 is OTP(one time programmable) 

04 f8 6c 18
92 1e 39 80
35 48 f2 03
2f ff ff fc

and page num 3 is not lock i can change the value like 0f ff ff f0 and show me that -ok-  and when after i read again the code i see that the code in page 3 dose not change page 0 to 2 is lock
and how can i erase page 3 and write it completly that can work ??

Re: right way to write to ultralight

You can not erase OTP bytes. The are one-time programmable. You can only ever *increase* them. That is to say if you have 0b00001110 in an OTP bytes, you can make it 0b11111111 or 0b00001111, but not 0b00000001 or 0b00000000.