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Nokia MBUS |
The following Information is gathered just by listening into the MBUS-Communication and
by guessing and trying a lot. No PICs has been read out or disassembled. No Nokia DLR-3p has been disassembled or sniffed by me.
Note: Nokia MBUS ist sometimes also called M2BUS. Do not confuse this whith
the I2C based Bus on some Motherboards.
Before you continue, you should get fimilar with the very basics of the MBUS-Protocol:
MBUS-Header (gnokii mailing list)
Message ID
some Protocol Info
TDMA/GSM FBUS/MBUS Site by arnu@flosys.com
Gnokii MBUS Code
The phone regulary sends the DLR3-Frame "1F,48,00,4E,00,02,01,xx,seq,checksum" to the µC in the dlr3-cable via MBUS, which devides into:
| Field size |
Description |
DLR3 data |
| 1 byte |
Protocol identifier - on MBUS always 0x1F |
1F |
| 1 byte |
Destination Addr |
48 |
| 1 byte |
Source Addr (00=Phone) |
00 |
| 1 byte |
Command |
4E |
| 2 bytes |
dl=data lenght |
00 02 |
| dl byte(s) |
Message Data, see below |
01 xx |
| 1 byte |
Sequence Number |
xx |
| 1 byte |
XOR Checksum |
xx |
The Cable should always anwser with a standard ack-message:
"1F,00,48,7F,seq,checksum". Always use the sequence number generated by the phone, but your own checksum.
With the "first version" DLR-3 Cable, I made some connections and created some stress-situations
to find out, how RTS,CTS, and the other Signals are coded into the last message byte.
| Bit Pos |
Description |
| 7 MSB |
always 0 |
| 6 |
always 0 |
| 5 |
always 0 |
| 4 |
always 0 |
| 3 |
??? looks like DSR, because it is 1 all the time |
| 2 |
0: Datamode, 1: Idle or Voicecall |
| 1 |
DCD; 1 if you have no connection, 0: CONNECT & CARRIER |
| 0 LSB |
CTS; 0 means, the PC is allowed to send data;
1 means, he PC have to wait
(for example while establishing a connection or when sending too much data at once) |
RTS Signaling
RTS is delivered to the phone via the XEAR pin. Pulling it low (through 1K) means, the phone is
allowed to send. Having it high, or letting it float will prevent the phone from
sending any data to the PC.
DTR: Connection Hangup and FBUS-Switch
For the DTR-Signal the XMIC-Pin is used. While it is usually used to
identify a DLR-3p cable to the phone, it can be used as DTR after the
MBUS-communication with the phone has been established.
Thanks to Anatoly Sudanov for the DTR-Info above!
Dropping DTR causes two things: a) an active dataconnection is
terminated, and b) the Serial-Pins are switched from AT-Mode to FBUS-Mode.
FOR PERSONAL USE ONLY
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