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Figure 25-3: CAN Core in Loopback Mode
CAN Controller
CAN_TXD
CAN_RXD
CAN Core
TX
RX
Combined Mode
The CAN controller is set in combined loopback and silent mode by programming the silent mode (
Silent
)
and loopback mode (
LBack
) bits in the test register (
CTR
) to 1. Combined mode can be used for testing
the CAN hardware without affecting other devices connected to the CAN bus. In this mode, the
CAN_RXD
pin is disconnected from the CAN core and the
CAN_TXD
pin is held high.
Figure 25-4: CAN Core in Combined Mode
CAN Controller
CAN_TXD
CAN_RXD
CAN Core
TX
RX
V
cc
L4 Slave Interface
The host processor accesses data, control, and status information of the CAN controller through the L4 slave
interface. The slave interface supports 32-bit accesses only.
This interface does not support error responses.
Note:
Clocks
The CAN controller operates on the
l4_sp_clk
and
can_clk
clock inputs. The
l4_sp_clk
clock is
used by the L4 slave interface and the
can_clk
is used to operate the CAN core.
The
can_clk
clock must be programmed to be at least eight times the CAN bus interface speed. For
example, for a CAN bus interface operating at a 1 Mbps baud rate, the
can_clk
clock must be set to at
least 8 MHz. The
l4_sp_clk
clock can operate at a clock frequency that is equal to or greater than the
can_clk
frequency.
Related Information
on page 2-1
For more information about the
l4_sp_clk
and
can_clk
clocks, refer to the
Clock Manager
chapter in
the
Cyclone V Device Handbook, Volume 3
.
Altera Corporation
CAN Controller Introduction
25-9
Combined Mode
cv_54025
2013.12.30