mcs7830 MosChip, mcs7830 Datasheet - Page 22

• Manufacturer Part Number: mcs7830
• Description: Usb-2.0 To Ethernet
• Manufacturer: MosChip

Page 22
MCS7830
USB-2.0 to Ethernet
Multicast Address Registers
(HIF_REG1 to HIF_REG8):
The Ethernet MAC receiver accesses these registers every time it receives a multi-cast or a broadcast frame. To
check whether the received multi-cast frame is valid, the Ethernet MAC does something called “hash fi ltering”.
In hash fi ltering, the CRC-32 (cyclic redundancy check) value is used. The six most signifi cant bits are taken
from the 32 bits of the CRC. The Ethernet MAC uses the higher three bits of the six bits as “HIF_ADDRESS”.
Three bits can have values from ‘000’ to ‘111’, which is a total of eight numbers. So the fi rst eight registers are
accessible by the Ethernet MAC. When the Ethernet MAC receives the contents of the register addressed by
it on the “HIF_DATA_OUT” (8 bits wide), it uses the remaining three bits of the six most signifi cant bits for bit
selection within the Byte.
The bits in the HIF Registers are arranged in an 8x8 matrix. The Ethernet MAC assumes the driver knows the
multi-cast addresses which are to be accepted. Depending on the multi-cast address, it calculates the 32-bit
CRC, and uses the six most signifi cant bits to arrange those values in such a way that the Ethernet MAC can
address any particular bit in the 8x8 matrix.
For the addresses the driver wants to accept, it writes a ‘1’ into those bit positions in the 8x8 matrix. The
Broadcast frame ‘1111_1111_1111’ is an all ‘1’ address, and is always accepted.
Inter-Packet Gap Registers
(HIF_REG9 & HIF_REG10):
These registers hold the IPG (Inter-Packet Gap) values. This is the amount of time between the end of the last
transmission and the start of the next one. The registers hold the number of clock cycles to wait. These values
must be multiplied by the clock period to obtain the actual amount of time to wait.
Address
Address
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
Multi-cast 0
Multi-cast 1
Multi-cast 2
Multi-cast 3
Multi-cast 4
Multi-cast 5
Multi-cast 6
Multi-cast 7
Field
IPG1
IPG
Field
R/W
R/W
HW
HW
R
R
R
R
R
R
R
R
R/W
R/W
SW
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
SW
Default
0x18
0x10
Default
0x00
0x00
0x00
0x00
0x00
0x00
0x00
0x00
Inter Packet Gap of 24 clocks
Inter Packet Gap of 16 clocks
Multi-cast Address. Byte 0
Multi-cast Address. Byte 1
Multi-cast Address. Byte 2
Multi-cast Address. Byte 3
Multi-cast Address. Byte 4
Multi-cast Address. Byte 5
Multi-cast Address. Byte 6
Multi-cast Address. Byte 7
Description
Description
Rev.
3.1