NEC Network Controller uPD98502 - Manual (Page 297)

CHAPTER 5 ETHERNET CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 297
5.2.30 En_RXFCR (Receive FIFO Control Register)
Bits Field R/W Default Description
31:26 UWM
[7:2]
R/W 30H Upper Water Mark:
This pointer is used with Auto Flow Control Enable bit in En_TXCR. When
the receiving data fill level exceeds this pointer, the transmit module
generates a flow control frame automatically.
25:24 Reserved R/W 0 Reserved for future use. Write 0s.
23:18 LWN
[7:2]
R/W 10H Lower Water Mark:
17:8 Reserved R/W 0 Reserved for future use. Write 0s.
7:2 RX_DRTH R/W 10H Receive Drain Threshold Level
This threshold is enable to the transmit data to the IBUS via internal DMAC
form the FIFO. Please see the Figure 5-3. This pointer is a word pointer.
1:0 Reserved R/W 0 Reserved for future use. Write 0s.
Figure 5-3. Rx FIFO Control Mechanism
DRTH
DRTH
DRTH
Rx_FIFO (256 Bytes)
DRTH
EOF
No Packet
data
Beginning
of the
frame
Request
to transmit
data
Request
to transmit
data
Receiving
frame
Received
End of frame
To internal bus From MAC Control Block
5.2.31 En_RXDPR (Receive Descriptor Pointer)
Bits Field R/W Default Description
31:2 RCVDP R/W 0 Receive Descriptor Pointer:
Please see the Section 5.3.5.
1:0 Reserved R/W 0 Reserved for future use. Write 0s.