ELM327P datasheet(24/51 Pages) ELM

24 / 51 page

24 of 51

ELM327

ELM327DSC

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Selecting Protocols

The ELM327 supports several different OBD

protocols (see Figure 2 below). As a user, you may

never have to choose which one it should use (since

the factory settings cause an automatic search to be

performed for you), but while experimenting, you may

want to specify which protocol is used.

For example, if you know that your vehicle uses

the SAE J1850 VPW protocol, you may want the

ELM327 to only try that protocol, and no others. If that

is what you want, simply determine the protocol

number (from the chart below), then use the ‘Set

Protocol’ AT Command as follows:

>AT SP 2

From this point on, the default protocol (used after

every power-up or AT D command) will be protocol 2

(or whichever one that you have chosen). Verify this

by asking the ELM327 to describe the current protocol:

>AT DP

SAE J1850 VPW

Now what happens if your friend has a vehicle that

uses ISO 9141-2? How do you use the ELM327

interface for that vehicle? There are a few choices...

One possibility is to change your protocol selection

to allow for the automatic searching for another

protocol, on failure of the current one. This is done by

putting an ‘A’ with the protocol number, as follows:

>AT SP A2

>AT DP

AUTO, SAE J1850 VPW

Now, the ELM327 will begin by trying protocol 2,

but will then automatically begin searching for another

protocol should an attempt to connect with protocol 2

fail (as would happen when you try to connect to the

friend’s vehicle). If you have the memory function

enabled when you connect to your friend’s vehicle,

their protocol will then be stored in memory as the new

default protocol, but that is only a minor inconvenience

as the next time you connect to your vehicle, it will try

the friends protocol, fail, and search until it finds yours.

Your protocol will then be resaved as the new default.

Perhaps you have disabled the memory function

(set pin 5 to 0V), and have used AT SP 2 to customize

the IC for your vehicle only, and you don’t want it to

search for others? (In effect, you have turned your

ELM327 into an ELM322 type interface.) In this case,

you might want to use the ‘Try Protocol’ command for

your friend’s vehicle, rather than setting it to something

permanently. You can either say:

>AT TP 3

if you already know that your friend’s vehicle uses

protocol 3, or else you can say:

>AT TP 0

which automatically tries all of the protocols (as

allowed by PP 07) looking for one that responds.

In general, users find that enabling the memory

(setting pin 5 to 5V) and choosing the ‘Auto’ option

(the easiest way is to say AT SP 0) works very well.

After the initial search, the protocol used by your

vehicle becomes the new default mode (so it is tried

first every time), and if the interface is used on another

vehicle, there is only a minor delay while it performs an

automatic search.

Figure 2. ELM327 Protocol Numbers

Description

SAE J1850 PWM (41.6 Kbaud)

Protocol

Automatic

SAE J1850 VPW (10.4 Kbaud)

ISO 9141-2 (5 baud init)

ISO 14230-4 KWP (5 baud init)

ISO 14230-4 KWP (fast init)

ISO 15765-4 CAN (11 bit ID, 500 Kbaud)

ISO 15765-4 CAN (29 bit ID, 500 Kbaud)

ISO 15765-4 CAN (11 bit ID, 250 Kbaud)

ISO 15765-4 CAN (29 bit ID, 250 Kbaud)

SAE J1939 CAN (29 bit ID, 250* Kbaud)

User1 CAN (11* bit ID, 125* Kbaud)

User2 CAN (11* bit ID, 50* Kbaud)

*user adjustable

ELM327P Datasheet(PDF) 24 Page - ELM Electronics

ELM327P Datasheet(HTML) 24 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Datasheet Download

Link URL