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AM79C976 Datasheet(PDF) 235 Page - Advanced Micro Devices |
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AM79C976 Datasheet(HTML) 235 Page - Advanced Micro Devices |
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235 / 309 page  8/01/00 Am79C976 235 P R E L I M INARY 7DEOH 5HFHLYH'HVFULSWRU 6:67</( 4 20 BAM 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). 4 19-18 TT[1:0] VLAN Tag Type. Indicates what type of VLAN tag, if any, is included in the received frame. 00 = Reserved 01 = Frame is Untagged 10 = Frame is Priority-tagged 11 = Frame is VLAN-tagged 4 17-16 Reserved. 4 15-0 BCNT 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. 8 31-0 RBADR[31:0] Receive Buffer Address. This field contains the address of the receive buffer that is associated with this descriptor. 0Ch 31:0 USER SPACE User Space. Reserved for user defined data. Offset Bit Name Description 031-0 RFRTAG[31:0] 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. 4 31-16 TCI[15:0] VLAN Tag Control Information copied from the received frame. 15-0 MCNT 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. 831 OWN This bit indicates whether the descriptor entry is owned by the host (OWN = 0) or by the Am79C976 controller (OWN = 1). The host sets the OWN bit after it has emptied the buffer pointed to by the descriptor entry. The Am79C976 controller clears the OWN bit after filling the buffer that the descriptor points to. Both the Am79C976 controller and the host must not alter a descriptor entry after it has relinquished ownership. 830 ERR Error Summary. ERR is the OR of FRAM, OFLO, and CRC. ERR is set by the Am79C976 controller and cleared by the host. 829 FRAM Framing error indicates that the incoming frame contains a non-integer multiple of eight bits and there was an FCS error. If there was no FCS error on the incoming frame, then FRAM will not be set even if there was a non-integer multiple of eight bits in the frame. FRAM is not valid in internal loopback mode. FRAM is valid only when ENP is set and OFLO is not. FRAM is set by the Am79C976 controller and cleared by the host. Offset Bit Name Description |
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