車両診断通信

Decomposition of SF-SF and MF-MF communications into type of frame.MF-MF communication behaves slightly differently in the BS and FS of FC.The parts of the message that are not included in the message for DLC reasons are filled in with padding.Any value can be used for padding.Commonly used values are 00, 55, AA, CC, and FF.

Four types of frames are explained.The first N_PCItype is available for immediate judgment upon reception.Each has its own unique parameters.SF.SF_DL.FF.FF_DL.FC.FS.BS.STmin.CF.SN.

CAN multiple frames can send/receive up to 4095 bytes.The parameter N_PCI is at the start of each frame, and there is a mechanism to concatenate the frames well.There are two main transmission methods depending on the number of data to be sent.If the number of data to be sent is 7 bytes or less, single frame transmission is used.If the number of transmitted data is 8 bytes or more, it is a multi-frame transmission.Multi-frame transmission has a mechanism to control the throughput by setting the CF transmission interval and the timing for receiving another FC with FC.

Extended addressing is an extended version of Normal addressing with N_TA added.Mixed addressing has 11bitID and 29bitID versions.The 11bitID (standard ID) version is based on Normal addressing and assumes gateway traversal.The 29bitID (extended ID) version is based on Normal fixed addressing and assumes gateway traversal.

Normal addressing is the simplest addressing format.Normal fixed addressing is the easiest addressing format to define as a specification

There are physical addresses for one-to-one communication and functional addresses for one-to-many communication.Physical and functional addresses are composed of four different addressing formatsThe addressing formats consist of N_AI, N_TAtype, N_TA, N_SA, and N_AE.However, they may or may not be used depending on the addressing format.

To determine the sampling points, the number of quantums in each segment must be determined.There are 4 types of segments, each for 1 bit.Synchronization Segment.Propagation Segment.Phase Segment1.Phase Segment2.Propagation Segment + Phase Segment1 is called tseg1, and Phase Segment2 is called tseg2

Basically, a Google search can provide information on the CAN data link layer.CAN baud rate setting is special.It is not possible to set the baud rate directly, but the quantum time, which is a decomposition of 1 bit, is determined first.Since the total quantum is the baud rate, it is necessary to calculate backward from the baud rate you want to set.CAN can adjust the sampling point.It can be decided at which quantum in the total quantum to sample.This is often expressed as [%].50[%] for the middle, 75[%] for slightly behind (around 3/4).

The required standard numbers were reviewed.CAN has become a relatively common specification, and you can find information there on the Internet and in books.1 Mbps is not often used in DoCAN.For legal reasons1Mbps lacks stability in some aspects.

The typical standards for vehicle diagnostic communication are ISO 15765-2 and ISO 14229-1.Depending on the manufacturer's policy, the standard number may be a requirement rather than a specific requirement.The layers of vehicle diagnostic communication can be represented by the OSI model.There are two main axes of vehicle diagnostic communication.UDS and OBD.OBD is referenced by vehicle emission regulations, so the various parameters are clear.UDS only has recommended values, and the actual values are dependent on the finished vehicle manufacturer.