C515C_9711 Datasheet, PDF (139/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.5 The On-Chip CAN Controller
The Controller Area Network (CAN) bus with its associated protocol allows communication between
a number of stations which are connected to this bus with high efficiency. Efficiency in this context
means:
– Transfer speed (data rates of up to 1 Mbit/sec can be achieved)
– Data integrity (the CAN protocol provides several means for error checking)
– Host processor unloading (the controller here handles most of the tasks autonomously)
– Flexible and powerful message passing (the extended CAN protocol is supported)
The CAN interface which is integrated in the C515C is fully compatible with the CAN module which
is available in the 16-bit microcontroller C167CR. This CAN module has been adapted with its
internal bus interface, clock generation logic, register access control logic, and interrupt function to
the requirements of the 8-bit C500 microcontroller architecture.
Generally, the CAN interface is made of two major blocks :
– The CAN controller
– The internal bus interface
The CAN controller is the functional heart which provides all resources that are required to run the
standard CAN protocol (11-bit identifiers) as well as the extended CAN protocol (29-bit identifiers).
It provides a sophisticated object layer to relieve the CPU of as much overhead as possible when
controlling many different message objects (up to 15). This includes bus arbitration, resending of
garbled messages, error handling, interrupt generation, etc. In order to implement the physical
layer, external components have to be connected to the C515C.
The internal bus interface connects the on-chip CAN controller to the internal bus of the
microcontroller. The registers and data locations of the CAN interface are mapped to a specific 256
byte wide address range of the external data memory area (XX00H to XXFFH) and can be
accessed using MOVX instructions.
Semiconductor Group
6-76
1997-11-01