dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 19

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

7 0 Packet Reception
Enabling the ST-NIC On An Active Network
After the ST-NIC has been initialized the procedure for dis-
abling and then re-enabling the ST-NIC on the network is
similar to handling Receive Buffer Ring overflow as de-
scribed previously
1 Program Command Register for page 0 (Command Reg-
2 Initialize Data Configuration Register (DCR)
3 Clear Remote Byte Count Registers (RBCR0 RBCR1)
4 Initialize Receive Configuration Register (RCR)
5 Place the ST-NIC in LOOPBACK mode 1 or 2 (Transmit
6 Initialize
7 Clear Interrupt Status Register (ISR) by writing 0FFH to
8 Initialize Interrupt Mask Register (IMR)
9 Program Command Register for page 1 (Command Reg-
ister
Configuration Register
(BNDRY)
(PSTOP)
it
ister
i
ii Initialize Multicast Address Registers (MAR0 – MAR7)
iii Initialize CURRent pointer
Initialize Physical Address Registers (PAR0 – PAR5)
e
e
21H)
61H)
Receive
Page Start (PSTART)
Buffer
e
02H or 04H)
Ring
(Continued)
Termination of Received Packet Packet Accepted
Boundary
and Page Stop
Pointer
19
10 Put ST-NIC in START mode (Command Register
11 Initialize the Transmit Configuration for the intended
END OF PACKET OPERATIONS
At the end of the packet the ST-NIC determines whether the
received packet is to be accepted or rejected It either
branches to a routine to store the Buffer Header or to anoth-
er routine that recovers the buffers used to store the packet
SUCCESSFUL RECEPTION
If the packet is successfully received the DMA is restored
to the first buffer used to store the packet (pointed to by the
Current Page Register) The DMA then stores the Receive
Status a Pointer to where the next packet will be stored
(Buffer 4) and the number of received bytes Note that the
remaining bytes in the last buffer are discarded and recep-
tion of the next packet begins on the next empty 256-byte
buffer boundary The Current Page Register is then initial-
ized to the next available buffer in the Buffer Ring (The
location of the next buffer had been previously calculated
and temporarily stored in an internal scratchpad register )
22H) The local receive DMA is still not active since the
ST-NIC is in LOOPBACK
value The ST-NIC is now ready for transmission and
reception
TL F 11157 – 14
e