MC68HC908AS60MFN MOTOROLA [Motorola, Inc], MC68HC908AS60MFN Datasheet - Page 334

• Manufacturer Part Number: MC68HC908AS60MFN
• Description: HCMOS Microcontroller Unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Byte Data Link Controller-Digital (BDLC-D)
21.4.1.6 Digital Loopback Mode
21.4.1.7 Analog Loopback Mode
Technical Data
334
When a bus fault has been detected, the digital loopback mode is used
to determine if the fault condition is caused by failure in the node’s
internal circuits or elsewhere in the network, including the node’s analog
physical interface. In this mode, the transmit digital output pin (BDTxD)
and the receive digital input pin (BDRxD) of the digital interface are
disconnected from the analog physical interface and tied together to
allow the digital portion of the BDLC to transmit and receive its own
messages without driving the J1850 bus.
Analog loopback mode is used to determine if a bus fault has been
caused by a failure in the node’s off-chip analog transceiver or
elsewhere in the network. The BDLC analog loopback mode does not
modify the digital transmit or receive functions of the BDLC. It does,
however, ensure that once analog loopback mode is exited, the BDLC
will wait for an idle bus condition before participation in network
communication resumes. If the off-chip analog transceiver has a
loopback mode, it usually causes the input to the output drive stage to
be looped back into the receiver, allowing the node to receive messages
it has transmitted without driving the J1850 bus. In this mode, the output
to the J1850 bus typically is high impedance. This allows the
communication path through the analog transceiver to be tested without
interfering with network activity. Using the BDLC analog loopback mode
in conjunction with the analog transceiver’s loopback mode ensures that,
once the off-chip analog transceiver has exited loopback mode, the
BCLD will not begin communicating before a known condition exists on
the J1850 bus.
Freescale Semiconductor, Inc.
For More Information On This Product,
Byte Data Link Controller-Digital (BDLC-D)
Go to: www.freescale.com
MC68HC908AS60 — Rev. 1.0
MOTOROLA