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CHAPTER 5 SAR FUNCTION
140
Word 0
The contents of Word 0 in the packet descriptor, read from system memory by
the
μ
PD98405, are stored as is. Word 0 must be initially cleared to all 0.
L
Bit used by the
μ
PD98405 as a flag. Set this bit to "1" as the initial value.
ABR
ABR bit.
This bit specifies whether the VC uses the ABR service.
1: ABR service
0: CBR, VBR, and UBR services
SHAPER NO.
Shaper number.
This field specifies the number of a shaper with which this VC is to be linked.
When the ABR bit is set to "1," this field has no meaning.
VPI/VCI
VPI/VCI field of cell header.
Tx QUEUE READ
POINTER
Pointer that indicates the first address of the next packet descriptor.
The initial value is set by the host. Packet descriptors must be allocated starting
from word boundaries. The two low-order bits of the address stored in this
pointer must, therefore, be 00. The
μ
PD98405 updates this pointer each time it
transmits a packet. Do not modify the value of this pointer other than when
performing initialization. Upon the termination of packet queue transmission, this
pointer points to an empty packet.
Rx VC TABLE
POINTER
Note
Pointer that indicates the address of the receive VC table.
This field is set with the VC NUMBER (excluding the lower 4 bits of the VC table
address) of the VC table used to receive a turn-around BRM cell. It is specified
when this VC uses the ABR service.
MCR
Note
Minimum cell rate.
This is specified when this VC uses the ABR service.
PCR
Note
Peak cell rate.
This is specified when this VC uses the ABR service.
ICR
Note
Initial cell rate.
This is specified when this VC uses the ABR service.
ACR
Note
Allowed cell rate.
This field must be set to the same initial value as that of the ICR. This is
specified when this VC uses the ABR service.
Note
The fields are used only by the VC which uses the ABR service. These fields must all be reset to "0" if
the ABR bit is "0."