Bosch TTCAN - Manual (Page 13)

User’s Manual
BOSCH - 13/77 -
Revision 1.6 TTCAN
11.11.02
manual_about.fm
2.3.4.4 Loop Back Mode
The CAN_Core can be set in Loop Back Mode by programming the Test Register bit LBack to
one. In Loop Back Mode, the CAN_Core treats its own transmitted messages as received
messages and stores them (if they pass acceptance filtering) into a Receive Buffer. Figure 3
shows the connection of signals CAN_TX and CAN_RX to the CAN_Core in Loop Back Mode.
Figure 3: CAN_Core in Loop Back Mode
This mode is provided for hardware self-test functions. To be independent from external
stimulation, the CAN_Core ignores acknowledge errors (recessive bit sampled in the
acknowledge slot of a data/remote frame) in Loop Back Mode. In this mode the CAN_Core
performs an internal feedback from its Tx output to its Rx input. The actual value of the
CAN_RX input pin is disregarded by the CAN_Core. The transmitted messages can be
monitored at the CAN_TX pin.
2.3.4.5 Loop Back combined with Silent Mode
It is also possible to combine Loop Back Mode and Silent Mode by programming bits LBack
and Silent to
one at the same time. This mode can be used for a “Hot Selftest”, meaning the
TTCAN hardware can be tested without affecting a running CAN system connected to the pins
CAN_TX and CAN_RX. In this mode the CAN_RX pin is disconnected from the CAN_Core
and the CAN_TX pin is held
recessive. Figure 4 shows the connection of signals CAN_TX and
CAN_RX to the CAN_Core in case of the combination of Loop Back Mode with Silent Mode.
Figure 4: CAN_Core in Loop Back combined with Silent Mode
CAN_TX CAN_RX
Tx Rx
CAN_Core
• •
TTCAN
CAN_TX CAN_RX
Tx Rx
CAN_Core
• •
=1
TTCAN