Nokia 21xx Communications Protocol

Serial Parameters

RTS and DTR must be logic 0 (voltage >= +10v) to provide power for the interface lead.

Protocol Details

Since communication occurs over a bidirectional 1 bit bus, a half duplex protocol is in operation.

Much of the data transfer is along the lines:

<computer sends request>

<phone sends ack>
<phone sends response>

<computer sends ack>

It is, however, possible for the phone to automatically send notification of certain events (e.g. the reception of a new SMS message) autonomously without a corresponding request from the computer. Thus, it is not safe
to assume the contents of a received message from the phone.

Shown below are the general formats for request, response and acknowledgement packets.

Request from Computer

+--+--+--+----------+--+---+
|00|ri|fl|data frame|id|chk|
+--+--+--+----------+--+---+

Ack from Phone

+--+--+--+------------+--+---+
|ri|00|fl|[data frame]|id|chk|
+--+--+--+------------+--+---+

Response from Phone

+--+--+--+----------+--+---+
|ri|00|fl|data frame|id|chk|
+--+--+--+----------+--+---+



     ri

    response identifier
    (corresponds to original request if appropriate) 0xe4 or 0xe0

     fl

    bytes in data frame
    - 1 (<= 0x78)

     data frame

    main body of response

     id

     response identity
    number 1..?, independently generated by phone

     chk

     checksum created
    by XORing all the preceding bytes in response

Ack from Computer

+--+--+--+--+---+
|00|ri|fl|id|chk|
+--+--+--+--+---+



     ri

     response identifier
    taken from response packet

     fl

     0x7f

     id

     response identity
    number 1..? corresponding to the response packet id

     chk

     checksum created
    by XORing all the preceding bytes in the ack

Request Sequence

Before free communication can occur the computer must send a special request for communication:

The complete packet is:

+--+--+--+--+--+--+--+--+--+--+--+
|00|f8|05|e9|00|02|1c|00|1c|01|17|
+--+--+--+--+--+--+--+--+--+--+--+

The phone will acknowledge with:

The complete acknowledgement packet is:

+--+--+--+--+--+--+--+--+
|f8|00|7e|1c|01|1c|02|85|
+--+--+--+--+--+--+--+--+