Thank you for your fast responses and excuse my late answer. I am now working (parallel) at a programming unit for my receiver memory.
Calculating a hex code from the 4-digit code and then just writing it to the receiver memory won't work.
From the limited testing I did myself, I found that if you write only the hex translation of the 4-digit code into memory it doesn't properly re-pair that key with the receiver. This is because during programming, the key also transmits two additional "rolling" codes which get written to other locations in the memory. Even if you know the 4-digit code of the key, there is no way to know what the two additional transmitted rolling codes will be (these are calculated by the key) so it is impossible to manually calculate and also write these to the memory. If the associated rolling codes aren't present in memory for a key then a remote signal from that key won't be accepted by the receiver. You will therefore have to physically program the key into the receiver using the normal programming procedure if you want it to work.
Okay I understand. But I don't want to reprogram an old key to make the key working. I want to reprogram the old key by writing the memory at the last key position, so that I can disable the pending alarm in the alarm unit with one of the remaining keys. In the 'anti theft device' description about the Alfa alarm (page 6) is explained that the alarm and the receiver works only together with the last code memorized to the receiver.
If your central locking is working remotely but the alarm isn't then you need to physically reprogram ALL your keys in again with the alarm switched ON at the keyswitch. The receiver will then resynchronise itself with the alarm box.
That is the bad news I have: I have tried to program with opening the memory. This opening of memorizing mode works with all three codes which are programmed and answers with the blinking LED, but no key is accepted. The receiver does not give the county code, it gives a 5 s constant light. It does not depend on alarm unit on or off. It is the same.
If that doesn't fix the problem then it means there is a key programmed into your receiver that you no longer have the actual key for.
Exactly the opposite: I am sure to know all codes of the receiver. I did not read the memory hex and tried to decode it. I made a 'brute force attack' to the receiver and tried the 10000 possible codes (0.0.0.0 to 18.104.22.168) by pressing the button and reading the led answer with the aid of a small interface and a micro controller. It took a quite long time (4 days), but the work did the controller.
In this case you will either need to program in an ADDITIONAL new key or you will need to clear all key codes already stored in memory and go through the physical reprogramming procedure again from scratch for ALL keys that you have (making sure the alarm remains switched ON at the key switch for the whole programming procedure).
Clearing all codes by only overwriting memory 0x04 to 0x1f with 0xff or blanking (with 0xff) all memory?
thank you for the tip with the code try. I will get some paper and work it out. - Be sure I will let you know, if I see no chance to find a solution.
I will post the content of my memory, because there will be a difference to other receivers. The receiver is obviously blocked to the programming of keys. I don't know the real reason for that, this was the condition I get the car back from my friendly Fiat dealer, including the red car room led blinking all the time in about 1 Hz frequency. I reset it myself with disconnecting the internal battery from the alarm unit. The dealer said, there was a broken fuse (can only be the permanent 12V), when he tried to fix my problem. But he could not fix it at all. Even I had to pay for.
greetings from now warmer north of Germany