C5 - Replacement Key / Key Plip Question

[sonoramicommando]

Ok, I've searched and found a few threads regarding this topic - but I'm stil unsure if consensus has been reached.
From the previous threads, the following is how I understand replacement key & plip process works - please confirm or correct as appropriately.

Key:
1) Buy a blank key from Citroen
2) Have the key cut per the original or 9-10 digit code comes in a little paper with a barcode
3) Have the key transponder chip for immobiliser programmed using credit card 4 digit security code and Lexia.

Plip:
1) Buy a new plip from Citroen OR a second hand plip from a wrecker
2) Have a blank key cut and programmed as above and install it to the plip
3) Have the plip central locking functions paired by:
a) Insert the key and the plip in the ignition
b) Turn the key to ignition
c) Press and hold one of the plip buttons for 10 odd seconds until central locking action occurs

Questions:

1) There are a read coil AND a write coil adjacent to the ignition key barrel. Is this correct?
If so,
2) Is the read coil for disabling immobiliser when a key with the matching code to the ECU is inserted in the barrel?
3) What is the write coil for? All I can think of is to write on the plip chip to match the central locking code for the ECU & BSI of a particular car.
Cheers,
Sam

[The Birdman]

Not really an answer to your specific questions but an observation in my opinion ,

as far as i am aware you cannot use a second hand transponder

and you need Planet/Lexia Diagnostics to code a key to your car ,

what you describe is the resynch method for an original key that is having problems being read by the car, more of a battery boost for the fob.

[wheeler]

Questions:

1) There are a read coil AND a write coil adjacent to the ignition key barrel. Is this correct?
If so,
2) Is the read coil for disabling immobiliser when a key with the matching code to the ECU is inserted in the barrel?
3) What is the write coil for? All I can think of is to write on the plip chip to match the central locking code for the ECU & BSI of a particular car.
Cheers,
Sam

1) Correct
2) Correct
3) Correct apart from it writes to the transponer chip not the plip.

Also you dont need to buy a blank key then get it cut, you cant order the keyblade already cut from citroen.

[sonoramicommando]

^ Thanks.
A couple more Q's:
- What is in the plip? Just a RF transmitter?
- Can any old plip (say, a second hand one from a wrecker) be paired to any car?
- If so, is it done using Lexia or just the central locking buttons?

Background info - The car came with one plip key and that's it. Me being forgetful and absent-minded person, I think it's prudent to have a spare. As the car came with a factory alarm, it would be best to have a second plip key to make full use of what I have.

Cheers,
Sam