NEC V850E/PH2, User Manual

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Chapter 18 AFCAN Controller
User’s Manual U16580EE3V1UD00
18.2 CAN Protocol
CAN (Controller Area Network) is a high-speed multiplex communication protocol for real-time commu-
nication in automotive applications (class C). CAN is prescribed by ISO 11898. For details, refer to the
ISO 11898 specifications.
The CAN specification is generally divided into two layers: a physical layer and a data link layer. In turn,
the data link layer includes logical link and medium access control. The composition of these layers is
illustrated below.
Figure 18-2: Composition of Layers
Note: CAN Controller specification
18.2.1 Frame format
(1) Standard format frame
• The standard format frame uses 11-bit identifiers, which means that it can handle up to 2,048
messages.
(2) Extended format frame
• The extended format frame uses 29-bit (11 bits + 18 bits) identifiers, which increases the
number of messages that can be handled to 2,048
×
2
18
messages.
• An extended format frame is set when “recessive level” (CMOS level of “1”) is set for both the
SRR and IDE bits in the arbitration field.
Phy s ic a l l a yer Pre s cription of s ign a l level a nd b it de s cription
D a t a link
l a yer Note
·
Logic a l link control (LLC)
·
Medi u m a cce ss control (MAC)
·
Accept a nce filtering
·
Overlo a d report
·
Recovery m a n a gement
·
D a t a c a p su led/not c a p su led
·
Fr a me coding ( s t u ffing/no s t u ffing)
·
Medi u m a cce ss m a n a gement
·
Error detection
·
Error report
·
Acknowledgement
·
S eri a ted/not s eri a ted
Higher
Lower