Motorola MC68824 User Manual page 48

3.2.1 LOAD INITIALIZATION TABLE FUNCTION CODE Command
The LOAD INITIALIZATION TABLE FUNCTION CODE command is the first command in the ini-
tialization sequence of the TBC. This command loads the 4-bit initialization table function code
through the data register (ORO) and sets the bus width to 8 or 16 bits. If function codes are not
used, no value needs to be loaded into ORO, however if the bus width is 16 bits this command
still needs to be issued. If the desired bus width is eight bits and no function codes are used, this
command is unnecessary. The only confirmation this command returns is an 'FF' in the semaphore
register. The coding for this command is DO or 01 and its format is shown below.
Where:
BUSW = Bus Width
0= 8-Bit Bus
1
I
1
1 = 16-Bit Bus
3.2.2 INITIALIZE Command
o
I
1
o
I
0
I
BUSW
I
INITIALIZE is the second command in the initialization sequence of the TBC. This command must
only be given while in the OFFLINE state after a RESET. Before giving this command, the host
must load the initialization table in shared memory and write the pointer for the initialization table
into the DR register.
The INITIALIZE command causes the TBC to load the initialization table pointer from the DR
register, load the private area function code and pointer from the initialization table, load the
operational TBC parameters from the initialization table, and initialize the private area. The TBC
also performs a self test of its internal resources upon execution of this command. The TBC will
return confirmation of this command in the CPA (offset 9C of the initialization table), provided
this word was cleared prior to command execution. If no errors are detected during the self test,
a value of one will be returned in the status word of the CPA. Otherwise, a value of 0011 hex will
be stored in the status word of the CPA. If a bus/address error occurs during execution of this
command, a severe interrupt will be generated requiring a RESET of the TBC. The coding for this
command is C7 and its format is shown below:
3
1
I
1
o
I
0
I
0
I
1
I
1
I
1
3.2.3 OFFLINE Command
The OFFLINE command causes the TBC to leave its present state and enter the OFFLINE state.
This command is typically used to end receive and transmit tests (see 3.6.3 FULL-DUPLEX LOOP-
BACK TEST Command and 3.6.4 TRANSMITTER TEST Command) and when the TBC is not in_ring.
Execution of this command clears the any_send_pending flag (IEEE 802.4 boolean) and resets the
receive and transmit machines.
If the TBC is transmitting when the OFFLINE command is issued, the current frame may not be
completed; that is, the end delimiter may not be sent. If the TBC is in_ring when this command
is given, the TBC will immediately drop out of the ring without notifying other stations or passing
the token. The OFFLINE command should only be issued when the TBC is in_ring if, for some
reason, the proper exit method is not successful. The proper way to eXit the ring is to issue the
STOP command, clear in_ring desired, and wait for a no_successor status from the TBC. Then
MC68824 USER'S MANUAL
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