CR16HCS5 Datasheet, PDF (111/156 Pages) National Semiconductor (TI) – Family of 16-bit CAN-enabled CompactRISC Microcontrollers

Setting the DDIR bit to “1” will cause the direction of the data
storage to be reversed — the last byte received is stored at
the highest address and the first byte is stored at the lowest
address. See Figure70 for illustration.
Sequence of Data Bytes on the Bus
ID
Data1 Data2 Data3 Data4 Data5 Data6 Data7 Data8 CRC
t
Storage of Data Bytes
in the Buffer Memory
ADDRoffset
0A₁₆
Data Bytes
Data8
Data7
08₁₆
Data6
Data5
06₁₆
Data4
Data3
04₁₆
Data2
Data1
Figure 70. Data Direction Bit set to ‘1’
LO
Listen Only — By setting the LO-bit to “1” the
CR16CAN interface is configured to behave
only as a receiver. This means:
• it cannot transmit any message.
• it cannot send a dominant ACK bit.
• when errors are detected on the bus, the
CR16CAN will behave as in the error pas-
sive mode.
Using this listen only function, the CR16CAN
interface can be adjusted when it gets connect-
ed to an operating network with unknown bus
speed.
IGNACK Ignore Acknowledge. If the ignore ACK func-
tion is enabled, then by setting the IGNACK bit
to “1”, CR16CAN does not expect to receive a
dominant ACK bit to indicate the validity of a
transmitted message. It will not send an error
frame when the transmitted frame in not ac-
knowledged by any other CAN node.
This feature can be used in conjunction with
the LOOPBACK option for stand-alone tests
outside of a CAN network.
LOOPBACK Loopback. By setting the LOOPBACK bit, all
messages sent by CR16CAN can also be re-
ceived by a CR16CAN buffer with a matching
buffer ID. However, CR16CAN does not ac-
knowledge a message sent by itself. Therefore
CR16CAN will send an error frame when no
other device connected to the bus has ac-
knowledged the message.
INTERNAL Internal. If the INTERNAL function is enabled,
the TX- and RX-pin of the CR16CAN are inter-
nally connected to each other. This feature can
be used in conjunction with the LOOPBACK
mode. This means that CR16CAN can receive
its own sent messages without connecting an
external transceiver chip to the RX- and TX-
pin; it allows the user to run real stand-alone
tests without any peripheral devices.
DIAGEN
EIT
Diagnostic Enable. The DIAGEN bit globally
enables or disables the special diagnostic fea-
tures of CR16CAN. This includes the following
functions:
• LO (Listen Only)
• IGNACK (Ignore Acknowledge)
• LOOPBACK (Loopback)
• INTERNAL (Internal Loopback)
• write access to hidden receive buffer
Error Interrupt Type. This bit configures when
the Error Interrupt Pending Bit (CIPND.EIPND)
is set and an error interrupt is generated if en-
abled by the Error Interrupt Enable
(CIEN.EIEN).
“0” The EIPND bit is set on every error on the
CAN bus.
“1” The EIPND bit is set only if the error state
(CSTPND.NS) changes as a result of in-
crementing either the receive or transmit
error counter.
111
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