Страница 1 мировой engineering стандарты общая спецификация

8.6.1 Service Description. 
The ReadDataByParameterIdentifier service provides a means for a tester to
request ECU data by Parameter Identifier (PID). A PID number is a unique 2-byte value that the ECU
translates into a specified piece of data (e.g., ABS left front wheel speed, or engine rpm). The length (number
of data bytes in the response message for a given PID) and scaling of the response data (associated with a
PID) must be documented in a CTS, SSTS, supplemental diagnostic specification, or another document or
database referenced by any of the proceeding documents. PID response data can range from one to seven
bytes in length per PID (not including the PID number).
Note: 
The 7-byte maximum results from the fact that PIDs can be packed into DPIDs and requested via the
$AA service. The $AA service uses UUDT responses. UUDT responses are limited to seven bytes. For the
purpose of service $22, the 7-byte maximum refers to the maximum number of bytes in the dataRecord for
each PID. Reference the positive response message definition table.
This service only provides a single USDT positive response to a request for one or multiple PIDs provided that
the request message is properly formatted and at least one of the requested PIDs is supported in the ECU. If a
tester needs to retrieve PID data periodically then the tester must first pack the PID (or PIDs) into a DPID via
the $2C service and then request the data periodically via the $AA service.
If a tester requests multiple PIDs with a single request of this service, the ECU shall include data in a positive
response for all of the PIDs that it supports. No data shall be included in a positive response for unsupported
PIDs, or for secure PIDs unless security access has been granted (ECU is unlocked) via service $27. See
paragraph 8.8 for more details on service $27.
A functional request for this service containing only unsupported PID(s) shall result in no response being sent.
A physically addressed request shall result in a negative response if none of the requested PIDs are supported
in the ECU.
The maximum number of PIDs that the ECU supports with a single request shall be documented in the ECU
CTS, SSTS, or supplemental diagnostic specification referenced by either of the preceding documents.
This service can also be used to retrieve emission related PIDs as specified in SAE J1979/ISO 15031-5.
Because SAE J1979/ISO 15031-5 uses a single byte PID number, a tool must request these emission PIDs
with the most significant byte (MSB) of the PID number set to $00 when using this service, to ensure request
message compatibility. See paragraph 8.6.5 for example.