Motorola MC68824 User Manual page 50

Sets the bus width to its default value (eight bits),
Resets the receive and transmit machines,
Sends silence symbols to the modem,
Zeros the internal TRT counter,
Zeros the internal copy of interrupt status word 0, and
Causes the TBC to believe the free FD pool is not empty and resets in_ring and NS known
(802.4 booleans).
After completing the above, the TBC sets the semaphore byte to IFF' hex when ready to receive
the LOAD INIT TABLE FC command. There is no other indication that the command has been
executed.
The coding for this command is IFF' and its format is shown below:
3
1
I
1
I
1 1
I
1
I
1
I
1
I
1
3.3 SET OPERATION MODE
The four commands in this category are used to set the various operation modes and options in
the TBC. The default setting is zero, or disabled, for all modes except for HLEN whose default is
one (see 3.3.3 SET MODE 3 Command). These commands are normally given only during ini-
tialization or testing.
3.3.1 SET MODE 1 Command
The default setting is zero for all modes described in this subsection. This command is normally
given only as part of an initialization sequence or during testing.
4 3 2 1 0
o
I
0
I
1
I
0
I
CUFC
I
CACF
I
lSTT
I
PDRF
CUFC - Recognize Frames with Undefined Frame Control (not part of IEEE 802.4)
1 Recognize frames with undefined frame control as valid data frames
o
Do not recognize frames with undefined frame control as valid data frames
When disabled, frames with undefined frame control fields are treated as noise bursts or
invalid frames and are not stored in memory. When enabled, the frames are treated as valid
data frames and the TBC can support additional frame control fields to be defined by the
user or by IEEE 802.4 in the future. This mode can also be useful in detecting error conditions
on the network.
CACF - Copy all Control Frames
1 Copy all control and data frames to queue six
o
Copy only data frames to the appropriate queue (normal operation)
In the CACF mode, all control and data frames are copied to the data buffers if the necessary
criteria for accepting a frame as in normal operation are met (destination address match,
etc.). This
mod~
is useful for monitoring network traffic. In this mode, all received frames
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