dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 21

• Manufacturer Part Number: dp83902a
• Description: St-nictm Serial Network Interface Controller For Twisted Pair
• Manufacturer: National Semiconductor Corporation

7 0 Packet Reception
REMOVING PACKETS FROM THE RING
Packets are removed from the ring using the Remote DMA
or an external device When using the Remote DMA the
Send Packet command can be used This programs the Re-
mote DMA to automatically remove the received packet
pointed to by the Boundary Pointer At the end of the trans-
fer the ST-NIC moves the Boundary Pointer freeing addi-
tional buffers for reception The Boundary Pointer can also
be moved manually by programming the Boundary Register
The ST-NIC knows the difference between an empty buffer
ring and a full buffer ring This situation is seen when the
Boundary Pointer (BNDRY) and the Current Page Pointer
(CURR) point to the same address If BNDRY caught up
with CURR the buffer is empty and if CURR caught up with
BNDRY the buffer is full
STORAGE FORMAT FOR RECEIVED PACKETS
The following diagrams describe the format for how re-
ceived packets are placed into memory by the local DMA
channel These modes are selected in the Data Configura-
tion Register
BOS
Series 32xxx or 680x0 processors
AD15
Receive Byte Count 1
e
Next Packet Pointer
0 WTS
Byte 2
e
1 in Data Configuration Register This format is used with
AD8 AD7
Receive Byte Count 0
(Continued)
Receive Status
1st Received Packet Removed by Remote DMA
Byte 1
AD0
21
BOS
680x0 type processors (Note The Receive Count ordering remains the
same for BOS
BOS
general 8-bit processors
AD15
Receive Byte Count 0
e
e
Next Packet Pointer
1 WTS
0 WTS
Byte 1
e
e
e
0 or 1 )
1 in Data Configuration Register This format is used with
0 in Data Configuration Register This format is used with
Receive Byte Count 0
Receive Byte Count 1
Next Packet Pointer
Receive Status
AD8 AD7
Byte 0
Byte 1
Receive Byte Count 1
Receive Status
Byte 2
TL F 11157 – 16
AD0