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Siemens P2 protocol
Looking for assistance on the Siemens P2 protocol...
By Richard Theron - FieldServer on 15 November, 2001 - 5:34 pm


I am looking for assistance on the Siemens P2 protocol.

- Is the P2 protocol open?
- If so were can the protocol specification document be obtained?


Alas, it is not open--perhaps more because I didn't document it very well than because it's any big secret.

But we do support more protocols than you can shake a stick at, including HTTP, OPC, Modbus, BACnet and Lon.

B.O. Nov. 13, 2001
Robert Old, System Architecture,
Siemens Building Technologies, Inc., Building Automation
1000 Deerfield Pkwy., Buffalo Grove, IL 60089-4513 USA
Phone: +1(847)941-5623, Fax: +1(847)919-8420


The Siemens P2 Protocol is anything but open. Getting any info on that is like pulling teeth. If you have any specific questions, give me a

Garry Cole

By pchipkin on 25 May, 2016 - 6:08 pm
1 out of 1 members thought this post was helpful...

I have source code for a driver I wrote in the early 90's to talk to a Siemens S5 PLC (I think). I had some info in german which I managed to use and a bit of observation & analysis got me to completion.

Trouble is I don't know if its P1 or P2. Any idea how to tell them apart.

1 out of 1 members thought this post was helpful...

Hi Peter,

The Siemens S5/S7 is a PLC protocol; very different. P1 is the "Floor Level Network" (FLN) used by controllers (MEC, MBC, SCU, PXC, etc.) to talk to the field gizmos (TECs, DPU, MPU, UC, etc..) It is RS-485, master-slave, half-duplex, and (of course) proprietary. P2 is the "Building level Network" (BLN) that their highest-level controllers (again, MEC, PXC, etc) use to talk to each other. It has several variants:

(1) "Pre-Apogee": RS-485, token-pass, used RAD-50 for text. Ancient; ignore

(2) "Apogee": RS-485, token-pass, used ASCII and longer names. Still a lot of stuff out there using it.

(3) "Apogee Ethernet": P2-protocol variant that uses Ethernet. Complicated and uses TCP/IP connections between every controller (oh, the horror!). Lots of it out there.

(4) "Apogee BACnet": new PXC, MEC, etc. can be ordered that talk BACnet/IP (Annex j) pretty well. Not much out there yet, but it is their new wave...

Hope this helps!