Skip to main content

Endiness of a System or Digital link

Endiness is characteristic of a Digital link or an Electronic System.

For a System, Endiness refers to the order in which the data is stored by the system in its memory. The order could be LSB to a lower memory address or MSB to lower memory address.

For example : A Data coming to system is  - 0x 00 FF
 - '00' : MSB and 'FF' : LSB in the received data.
 - System use 2 bytes to store data in its memory. Suppose address bytes 0x0001 and 0x0002 are to be used for storing these 2 data bytes.
- Strange thing is , System can utilize these two bytes in two ways to store the data.

Method 1  : Little Endian
Address  | 0x0001          |   0x0002     |
Data        |   LSB - FF    |    MSB - 00 |

Method 2 : Big Endian
Address  | 0x0001          |   0x0002     |
Data        |   LSB - 00    |    MSB - FF |

For a communication link like CAN , Ethernet ,  an endiness of a channel means , the order in which  data is put on the bus.

Comments

Post a Comment

Popular posts from this blog

What is UDS on CAN or Diagnostic on CAN ?

OSI Model and Diagnostics : OSI model has 7 layers and each layer has defined functionality. To understand this you can refer this excellent IEEE  publication. It explains OSI Model for CAN , Ethernet, flexray and MOST.  External reference : http://www.ieee802.org/1/files/public/docs2013/new-tsn-diarra-osi-layers-in-automotive-networks-0313-v01.pdf   So let us understand,  what is this UDS on CAN  ? When a Diagnostic Message formatted  as per ISO 14229 -1 i.e UDS Standard is sent over Controller Network we say Diagnostics Communication is happening as per UDS on CAN. So as per this : Below layers participate in Diagnostic Communication Over CAN :  1. Application Layer :  ISO 14229-1:2013 ROAD VEHICLES — UNIFIED DIAGNOSTIC SERVICES (UDS) — PART 1: SPECIFICATION AND REQUIREMENTS  ISO 14229-3:2012 ROAD VEHICLES — UNIFIED DIAGNOSTIC SERVICES (UDS) — PART 3: UNIFIED DIAGNOSTIC SERVICES ON CAN IMPLEMENTATION (UDSON...
Post a Comment
Read more

Diagnostic Session Function 3 - Security and authorization of the user – Use of Seed and Key for authenticating -

 Let us see how the function of Security Access is served by Diagnostic Session.   Security is an important aspect of an UDS implementation. It is required to avoid unauthorized access to ECU. As one can control ECU functionality through usage of UDS services, it becomes vital to secure ECU from unintended or vulnerable access.  Hence UDS has provisioned a special service called Security Access SID 0x27 to authorize a user.It works on the principle of Seed and key mechanism. You can get lot many websites explaining how security service works. The intention of this write up is to know how session is important for the implementation of security of an ECU. As mentioned in the blog (https://thevehiclediagnostics.blogspot.com/2020/01/what-is-diagnostic-session.html )  a diagnostic session of an ECU is a timed window. Session management helps in following manner for security 1 . Limit a secured access for timed window i.e session. 2 . End se...
Post a Comment
Read more

Diagnostic Session : Function 5 - Session Oriented Access to Services

  There are multiple users those need to use UDS protocol for various purposes like Garage person for fault detection, ECU manufacture for Testing activities and development purpose. Also  OEM needs  access to ECU memory for flashing purposes.   UDS services can be categorized in different groups like few services will just read some Data from memory,a few will write or update the data to memory, some will erase/update ECU sw itself , some will control Inputs outs of ECU directly.  So there are chances that any improper usage of UDS service may result in safety issues , security breaches or damage to ECU resources. Hence, it doesn't make sense to give access to all services to everyone. To achieve this UDS has designed some mechanisms like Sessions, Security Authentication, Preconditions. I hope you are aware about what a Diagnostic Session is. Please visit :  https://thevehiclediagnostics.blogspot.com/2020/01/what-is-diagnostic-session.html   if you ...
Post a Comment
Read more