Master Request Frame / Slave Response Frame

The protocol defines two diagnostic frames: the master request frame and the slave response frame. They are defined based on the ISO 15765-2 transport and on uniform diagnostic services (UDS) in accordance with ISO 14229. A master request frame is usually used as a diagnostic request or to configure slaves. A slave response frame is used as a diagnostic response.

Functionality

Like unconditional, event triggered and sporadic frames, the two diagnostic frames are composed of a Frame Header and a Frame Response. In the case of a master request frame (diagnostic request), the master transmits both the frame header and the frame response. The frame header is transmitted with ID=0x3C. In the case of a slave response frame (diagnostic response), the master sends the frame header, and the diagnosed slave sends the frame response. The frame header is sent with ID=0x3D (see figure: Diagnostic Principle).