LAN91C94 datasheet(43/120 Pages) SMSC

43 / 120 page

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OFFSET

NAME

MEMORY CONFIGURATION

TYPE

Lower Byte - READ/WRITE

Upper Byte - READ ONLY

SYMBOL

MCR

HIGH

BYTE

MEMORY SIZE MULTIPLIER M

LOW

BYTE

MEMORY RESERVED FOR TRANSMIT (in bytes x 256 x M)

MEMORY

RESERVED

FOR

TRANSMIT

Programming this value allows the host CPU to

reserve memory to be used later for transmit,

limiting the amount of memory that receive

packets can use up.

When

programmed

for

zero,

the

memory

allocation between transmit and receive is

completely dynamic.

When programmed for a non-zero value, the

allocation is dynamic if the free memory

exceeds the programmed value, while receive

allocation requests are denied if the free

memory is less or equal to the programmed

value.

This register defaults to zero upon reset. It is not

affected by the RESET MMU command.

The value written to the MCR is a reserved

memory

space

ADDITION

ANY

MEMORY CURRENTLY IN USE. If the memory

allocated for transmit plus the reserved space

for transmit is required to be constant (rather

than grow with transmit allocations) the CPU

should update the value of this register after

allocating or releasing memory.

The contents of MIR as well as the low byte of

MCR are specified in 256 x M bytes.

The

multiplier M is determined by bits 11,10,and 9

as follows. Bits 11,10 and 9 are read only bits

used by the software driver to transparently run

on different controllers of the LAN9000 family:

DEVICE

BIT 11

BIT 10

BIT 9

MAX MEMORY SIZE

LAN91C100

256 x 256 x 2=128k

LAN91C90

256 x 256 x 1 =64k

FUTURE

256k

" "

512k

" "

LAN91C94 Datasheet(PDF) 43 Page - SMSC Corporation

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