ENC28J60
TABLE 7-3:
Bit
RECEIVE STATUS VECTORS
Field
Description
31
30
29
Zero
0
Receive VLAN Type Detected
Receive Unknown Opcode
Current frame was recognized as a VLAN tagged frame.
Current frame was recognized as a control frame but it contained an
unknown opcode.
28
27
26
Receive Pause Control Frame
Receive Control Frame
Dribble Nibble
Current frame was recognized as a control frame containing a valid pause
frame opcode and a valid destination address.
Current frame was recognized as a control frame for having a valid
type/length designating it as a control frame.
Indicates that after the end of this packet, an additional 1 to 7 bits were
received. The extra bits were thrown away.
25
24
23
22
21
Receive Broadcast Packet
Receive Multicast Packet
Received Ok
Indicates packet received had a valid broadcast address.
Indicates packet received had a valid multicast address.
Indicates that at the packet had a valid CRC and no symbol errors.
Indicates that frame type/length field was larger than 1500 bytes (type field).
Length Out of Range
Length Check Error
Indicates that frame length field value in the packet does not match the
actual data byte length and specifies a valid length.
20
CRC Error
Indicates that frame CRC field value does not match the CRC calculated
by the MAC.
19
18
Reserved
Carrier Event Previously Seen
Indicates that at some time since the last receive, a carrier event was
detected. The carrier event is not associated with this packet. A carrier
event is activity on the receive channel that does not result in a packet
receive attempt being made.
17
16
Reserved
Long Event/Drop Event
Indicates a packet over 50,000 bit times occurred or that a packet was
dropped since the last receive.
15-0 Received Byte Count
Indicates length of the received frame. This includes the destination
address, source address, type/length, data, padding and CRC fields. This
field is stored in little-endian format.
In the event that the application needed to do random
access to the packet, it would be necessary to manu-
ally calculate the proper ERDPT, taking care to not
exceed the end of the receive buffer if the packet spans
the ERXND-to-ERXST buffer boundary. In other words,
given the packet start address and a desired offset, the
application should follow the logic shown in
Example 7-1.
7.2.3
READING RECEIVED PACKETS
To process the packet, the host controller will normally
use the RBM SPI command and start reading from the
beginning of the next Packet Pointer. The host controller
will save the next Packet Pointer, any necessary bytes
from the receive status vector and then proceed to read
the actual packet contents. If ECON2.AUTOINC is set, it
will be able to sequentially read the entire packet without
ever modifying the ERDPT registers. The Read Pointer
would automatically wrap at the end of the circular
receive buffer to the beginning.
EXAMPLE 7-1:
RANDOM ACCESS ADDRESS CALCULATION
if Packet Start Address + Offset > ERXND, then
ERDPT = Packet Start Address + Offset – (ERXND – ERXST + 1)
ERDPT = Packet Start Address + Offset
else
DS39662B-page 44
Preliminary
© 2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
