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NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
- 776 -
Revision V1.30
NUC97
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of the combination of Loop Back Mode with Silent Mode.
C_CAN
= 1
CAN_TX
CAN_RX
CAN_Core
Tx
Rx
Figure 5.24-4 CAN Core in Loop Back Mode Combined with Silent Mode
Basic Mode
5.24.6.4
The CAN Core can be set in Basic Mode by programming the Test Register bit Basic to one. In this
mode, the C_CAN runs without the Message RAM.
The IF1 Registers are used as Transmit Buffer. The transmission of the contents of the IF1 Registers
is requested by writing the Busy bit of the IF1 Command Request Register to one. The IF1 Registers
are locked while the Busy bit is set. The Busy bit indicates that the transmission is pending.
As soon the CAN bus is idle, the IF1 Registers are loaded into the shift register of the CAN Core and
the transmission is started. When the transmission has been completed, the Busy bit is reset and the
locked IF1 Registers are released.
A pending transmission can be aborted at any time by resetting the Busy bit in the IF1 Command
Request Register while the IF1 Registers are locked. If the software has reset the Busy bit, a possible
retransmission in case of lost arbitration or in case of an error is disabled.
The IF2 Registers are used as a Receive Buffer. After the reception of a message the contents of the
shift register is stored into the IF2 Registers, without any acceptance filtering.
Additionally, the actual contents of the shift register can be monitored during the message transfer.
Each time a read Message Object is initiated by writing the Busy bit of the IF2 Command Request
Register to one, the contents of the shift register are stored into the IF2 Registers.
In Basic Mode, the evaluation of all Message Object related control and status bits and the control bits
of the IFn Command Mask Registers are turned off. The message number of the Command request
registers is not evaluated. The NewDat and MsgLst bits in the IF2 Message Control Register retain
their function, DLC3-0 indicates the
received DLC, and the other control bits are read as ‘0’.
Software Control of CAN_TX Pin
5.24.6.5
Four output functions are available for the CAN transmit pin, CAN_TX. In addition to its default
function (serial data output), the CAN transmit pin can drive the CAN Sample Point signal to monitor
CAN_Core’s bit timing and it can drive constant dominant or recessive values. The latter two
functions, combined with the readable CAN receive pin CAN_RX, can be used to check the physical
layer of the CAN bus.
The output mode for the CAN_TX pin is selected by programming the Tx1 and Tx0 bits of the CAN
Test Register.
The three test functions of the CAN_TX pin interfere with all CAN protocol functions. CAN_TX must be
left in its default function when CAN message transfer or any of the test modes (Loop Back Mode,