DP83907 datasheet(45/70 Pages) NSC

45 / 70 page

60 Operation of DP83907 (Continued)

TLF12082 – 28

FIGURE 33 Received Packet Aborted

if it Hits Boundary

Enabling the DP83907 on an Active Network

After the DP83907 has been initialized the procedure for

disabling and then re-enabling the DP83907 on the network

is similar to handling Receive Buffer Ring overflow as de-

scribed previously

1) Program Command Register for page 0 (Command

2) lnitialize Data Configuration Register (DCR)

3) Clear Remote Byte Count Registers (RBCR0 RBCR1)

if using Remote DMA

4) lnitialize Receive Configuration Register (RCR)

5) Place the DP83907 in LOOPBACK mode 1 or 2 (Trans-

mit Configuration Register e 02H or 04H)

6) Initialize

Receive

Buffer

Ring

Boundary

Pointer

(BNDRY)

Page Start (PSTART)

and Page Stop

(PSTOP)

7) CIear Interrupt Status Register (ISR) by writing OFFH to

8) lnitialize Interrupt Mask Register (IMR)

9) Program Command Register for page 1 (Command

i) Initialize Physical Address Registers (PAR0 – PAR5)

ii) Initialize

Multicast

Address

Registers

(MAR0 –

MAR7)

iii) Initialize CURRENT pointer

10) Put DP83907 in START mode (Command Register e

22H) The local receive DMA is still not active since the

DP83907 is in LOOPBACK

11) Initialize the Transmit Configuration for the intended

value The DP83907 is now ready for transmission and

reception

End of Packet Operations

At the end of the packet the DP83907 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

TLF12082 – 29

FIGURE 34 Termination of Received

Packet-Packet Accepted

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)

Buffer Recovery for Rejected Packets

If the packet is a runt packet or contains CRC or Frame

Alignment errors it is rejected The buffer management log-

ic resets the DMA back to the first buffer page used to store

the packet (pointed to by CURR) recovering all buffers that

had been used to store the rejected packet This operation

will not be performed if the DP83907 is programmed to ac-

cept either runt packets or packets with CRC or Frame

Alignment errors The received CRC is always stored in

buffer memory after the last byte of received data for the

packet

TLF12082 – 30

FIGURE 35 Termination of Receive

Packet-Packet Reject

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