Motorola MC68824 User Manual page 70

be cleared only when the TBC actually executes the command. A situation may arise in which
the CPU may get an interrupt without any status bits in the interrupt status words being set. This
scenario may occur if the host happens to be issuing a CLEAR INTERRUPT STATUS command
right after the TBC has updated one of the interrupt status words for a new event but before the
TBC generated an IRQ. If that situation occurs the host should issue the CLEAR INTERRUPT
STATUS COMMAND with a zero mask in CPA VALO and CPA VAL 1. Note that the TBC command
complete bit (TCC) residing in interrupt status word 0 is not set after completion of this command.
The coding of this command is 88 and its format is shown below:
1
I
0
I
0
o
I
1
o
I
0
I
0
3.7.2 RESPONSE READY Command
This command is used by the host to notify the TBC that a response frame is ready to be transmitted
following the reception of a request with response frame. The issuance of this command is an
indication to the TBC that the response pointer in the initialization table located at offset 88 is
valid. This command is only applicable when not in predefined response mode, see 4.5 RECEPTION
OF RWR FRAMES AND TRANSMISSION OF RESPONSE for a description of this mechanism.
The coding for this command is C5 and its format is shown below:
1
I
1
I
0
I
0
I
0
I
1
I
0
I
1
3.8 MODEM CONTROL
Two commands are provided to allow the TBC to communicate management services to the
physical layer of the network.
3.8.1 PHYSICAL Command
This command is used by the host processor to control the modem while in station management
and should only be given when the TBC is in the OFFLINE state. Status is returned to the last
word in the command parameter area (CPA RESULT) as shown following the command format.
The physical data request channel is fully described in 5.9.1 Physical Data Request Channel while
the physical data indication channel is described in 5.9.2 Physical Data Indication Channel. Note
that SMREQ equals zero is an indication that station management has been selected. This signal
is automatically asserted when the first physical command is issued by the host. SMREQ will stay
low until the END PHYSICAL command (see 3.8.2 END PHYSICAL Command) is issued by the
host to terminate station management. SMREQ is also referred as TXSYM3 in the 802.4G docu-
ment.
The coding for the physical command is A1-A7 and its format is shown below:
2 1 0
o
I
DATA
I
TXSYM2
I
TXSYMl
MC68824 USER'S MANUAL MOTOROLA
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