MC68HC08AS32 Datasheet, PDF (329/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Byte Data Link Controller-Digital (BDLC-D)
BDLC MUX Interface
20.4.1.7 Analog Loopback Mode
Analog loopback 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 BCLD 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 is typically 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.
20.5 BDLC MUX Interface
The MUX interface is responsible for bit encoding/decoding and digital
noise filtering between the protocol handler and the physical interface.
TO CPU
CPU INTERFACE
PROTOCOL HANDLER
MUX INTERFACE
PHYSICAL INTERFACE
BDLC
TO J1850 BUS
Figure 20-3. BDLC Block Diagram
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Byte Data Link Controller-Digital (BDLC-D)
Advance Information
329