LAN91C111 datasheet(40/125 Pages) MICROCHIP

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LAN91C111

DS00002276A-page 40

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HASH VALUE - Provides the hash value used to index the Multicast Registers. Can be used by receive routines to speed

up the group address search. The hash value consists of the six most significant bits of the CRC calculated on the Des-

tination Address, and maps into the 64 bit multicast table. Bits 5,4,3 of the hash value select a byte of the multicast table,

while bits 2,1,0 determine the bit within the byte selected. Examples of the address mapping:

MULTCAST - Receive frame was multicast. If hash value corresponds to a multicast table bit that is set, and the address

was a multicast, the packet will pass address filtering regardless of other filtering criteria.

8.3

I/O Space

The base I/O space is determined by the IOS0-IOS2 inputs and the EEPROM contents. To limit the I/O space require-

ments to 16 locations, the registers are assigned to different banks. The last word of the I/O area is shared by all banks

and can be used to change the bank in use. Registers are described using the following convention:

FFSET - Defines the address offset within the IOBASE where the register can be accessed at, provided the bank select

has the appropriate value.

The offset specifies the address of the even byte (bits 0-7) or the address of the complete word.

The odd byte can be accessed using address (offset + 1).

Some registers (like the Interrupt Ack., or like Interrupt Mask) are functionally described as two eight bit registers, in that

case the offset of each one is independently specified.

Regardless of the functional description, all registers can be accessed as doublewords, words or bytes.

The default bit values upon hard reset are highlighted below each register.

Address

Hash Value 5-0

Multicast Table Bit

ED 00 00 00 00 00

0D 00 00 00 00 00

01 00 00 00 00 00

2F 00 00 00 00 00

000 000

010 000

100 111

111 111

MT-0 bit 0

MT-2 bit 0

MT-4 bit 7

MT-7 bit 7

OFFSET

NAME

TYPE

SYMBOL

HIGH

BYTE

bit 15

bit 14

bit 13

bit 12

bit 11

bit 10

bit 9

bit 8

XXX

LOW

BYTE

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

XXX

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