mcs7830 MosChip, mcs7830 Datasheet - Page 20

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

Page 20
MCS7830
USB-2.0 to Ethernet
Description of Programmable Registers
(HIF Registers)
HIF registers are the Host Interface registers, and these
are a part of the Ethernet MAC design. The registers
are written into and read from the bridge side by using
the WR_DB and RD_DB signals. The bridge uses a
4-bit address bus ‘ADDRESS_DB’. On the Ethernet
MAC side (receiver), the HIF Registers are read using
a 3-bit address bus which is used to access the fi rst
eight registers. A “HIF_ADDRESS_RD” signal is used
to validate the address. 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.
The address and the number of the HIF Registers are
not the same. The address for Register-1 is 0x0000;
Register-2 is 0x0001; and so on.
HIF Registers 1 through 8 are used for hash fi ltering.
HIF Registers 9 & 10 are used for IPG & IPG1 (Inter
Packet Gap). This is confi gurable (refer to the 802.3
specifi cation).
HIF Registers 11 & 12 are used as the MIIM_DR data
register (data to be written into MIIM (PHY) ).
HIF Registers 13 & 14 are used as the MIIM_CR
command register (commands for accessing the MIIM
registers).
HIF Register 15 is the MIIM (PHY) Confi guration
Register.
HIF Registers 16 through 21 hold the Ethernet MAC
Address (Station Address).
Rev.
3.1