lan91c100 Standard Microsystems Corp., lan91c100 Datasheet - Page 29

• Manufacturer Part Number: lan91c100
• Description: Feast ? Ast Ethernet Controller
• Manufacturer: Standard Microsystems Corp.

I/O SPACE - BANK 0
MEMORY
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.
zero, the memory allocation between transmit
and receive is completely dynamic.
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.
BYTE
BYTE
HIGH
LOW
OFFSET
A
RESERVED
LAN91C100
LAN91C90
FUTURE
FUTURE
FUTURE
DEVICE
0
0
MEMORY CONFIGURATION REGISTER
When programmed for
0
0
FOR
MEMORY RESERVED FOR TRANSMIT (IN BYTES * 256 * M)
bit 11
0
0
0
1
1
TRANSMIT
NAME
Bit 10
1
0
1
0
1
0
0
When
bit 9
0
1
1
0
1
29
1
0
The value written to the MCR is a reserved
memory
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 * M bytes.
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):
16
M
2
1
4
8
MEMORY SIZE MULTIPLIER
0
0
space
MAX MEMORY SIZE
READ/WRITE
Lower Byte -
Upper Byte -
READ ONLY
256*256*2=128k
256*256*1=64k
TYPE
(M)
1
0
IN
256k
512k
1M
ADDITION
0
0
SYMBOL
MCR
TO
1
0
ANY
The