Service Interaction Protocol

Periodic Read

0x2A

Protocol Identifier

Requests periodic transmission of data from an ECU at specified intervals, enabling continuous monitoring of dynamic vehicle parameters.

A Service Identifier (SID) is a single-byte value (0x00–0xFF) in position 0 of every UDS request frame. It specifies which diagnostic operation the client wishes the ECU to execute. The positive response echoes the SID with the high bit set (SID + 0x40).

DATA_MODEL

PUSH_STREAM

The ECU autonomously broadcasts data frames without intermediate requests.

SCHEDULER

DYNAMIC

Supports multiple identifiers with different frequencies (Slow, Medium, Fast).

TIMEOUT

P3_DRIVEN

Streaming persists as long as the tester is present (S3 timer logic).

Overview

ISO 14229-1

“The ReadDataByPeriodicIdentifier service is used by the client to request periodic transmission of data record values of data identifiers from the server.”

Continuous Monitoring

Real-time RPM/Speed logging
Dynamic sensor calibration
Oscilloscope-style data viewing
Diagnostic logging sessions

Dependencies

TesterPresent (0x3E) required for long sessions
Extended Session (0x03) usually required
PDID must be defined in ECU table

Default Behavior

At startup, no periodic data transmission is active. Once a client successfully requests a PDID, the ECU will continue to stream data at the requested rate until a “Stop” request (Mode 0x04) is received, the diagnostic session is reset, or the ECU is power-cycled.

Protocol Anatomy (Subscribe Fast)

◆ PROTOCOL ANATOMY

View

REQUEST_TX

0x2A PERIODIC READ

RESPONSE_RX

0x2A RESPONSE

Transmission Modes

The first parameter defines how fast the ECU should sample and send the data.

Mode	Name	Typical Frequency	Use Case
0x01	Slow Rate	1-2 Hz	Temp, Battery Level
0x02	Medium Rate	5-10 Hz	Vehicle Speed, O2 Sensors
0x03	Fast Rate	20-100 Hz	Crank Sensor, Torque
0x04	Stop Sending	N/A	Explicit termination

Message Format

Request Format

Byte	Field	Value	Description
0	SID	0x2A	Read Data Periodic
1	Mode	0x01-04	Transmission rate
2	PDID #1	0xNN	Periodic Data ID
3	PDID #N	...	Optional extra IDs

Periodic Response

Click to Enlarge

Mechanism for continuous real-time data push from ECU to tester.

tip _entry

Note: The ECU sends multiple responses for a single request!

Byte	Field	Value	Description
0	Response SID	0x6A	Positive Response
1	PDID	0xNN	Identifier of the data
2-N	Data	...	The actual payload

Examples

Workflow: Dynamic Data Streaming

6 steps

Tester

ECU

Start RPM Streaming (Medium Rate)

tx_packet

Request

2A 02 01

> Start PDID 0x01 at Medium Rate

rx_packet

Periodic #1

6A 01 0B B8

> RPM = 3000 (0x0BB8)

rx_packet

Periodic #2

6A 01 0B BA

> RPM = 3002 (sent ~100ms later)

Stop Streaming

tx_packet

Request

2A 04 01

> Stop PDID 0x01

rx_packet

Response

6A

> Confirmation: Stopped

Negative Response Codes

Error_Catalog

Negative Response Codes

THREAT_LEVEL3 HIGH2 MEDIUM5 NRCs TOTAL

ISO_14229_ANNEX_ANRC_ENGINE_V2