AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 231

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

8/01/00
Offset
0Ch
4
4
4
4
8
19-16
30-16
15-0
15-0
31:0
Bit
21
20
31
RFRTAG[14:0]
USER SPACE
MCNT
Name
LAFM
BCNT
BAM
Logical Address Filter Match is set by the Am79C976 controller when it accepts the
received frame based on the value in the logical address filter register. LAFM is valid
only when ENP is set. LAFM is set by the Am79C976 controller and cleared by the
host.
Note that if DRCVBC (CSR15, bit 14) is cleared to 0, only BAM, but not LAFM will be
set when a Broadcast frame is received, even if the Logical Address Filter is
programmed in such a way that a Broadcast frame would pass the hash filter. If
DRCVBC is set to 1 and the Logical Address Filter is programmed in such a way that
a Broadcast frame would pass the hash filter, LAFM will be set on the reception of a
Broadcast frame.
This bit does not exist when the Am79C976 controller is programmed to use 16-bit
software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is
cleared to 0).
Broadcast Address Match is set by the Am79C976 controller when it accepts the
received frame, because the frame’s destination address is of the type ’Broadcast.’
BAM is valid only when ENP is set. BAM is set by the Am79C976 controller and
cleared by the host.
This bit does not exist when the Am79C976 controller is programmed to use 16-bit
software structures for the descriptor ring entries (BCR20, bits 7-0, SWSTYLE is
cleared to 0).
Reserved.
Buffer Byte Count is the length of the buffer pointed to by this descriptor, expressed
as the two’s complement of the length of the buffer. This field is written by the host
and unchanged by the Am79C976 controller.
Reserved.
Receive Frame Tag. Indicates the Receive Frame Tag applied from the EADI
interface. This field is user defined and has a default value of all zeros. When
RXFRTG (CSR7, bit 14) is set to 0, RFRTAG will be read as all zeros. See the section
on Receive Frame Tagging for details.
Message Byte Count is the number of bytes of the received message written to the
receive buffer. This is the actual frame length (including FCS) unless stripping is
enabled and the length field is < 46 bytes. In this case, MCNT is 14 + length_field.
MCNT can take values in the range 15 to 59 and values greater than or equal to 64.
MCNT is expressed as an unsigned binary integer. MCNT is valid only when ERR is
clear and ENP is set. MCNT is written by the Am79C976 controller and cleared by
the host.
User Space. Reserved for user defined data.
P R E L I M I N A R Y
Am79C976
Description
231