LAN91C94 datasheet(46/120 Pages) SMSC

46 / 120 page

I/O SPACE - BANK1

OFFSET

NAME

BASE ADDRESS REGISTER

TYPE

READ/WRITE

SYMBOL

BAR

In ISA mode, this register holds the address decode options chosen for the I/O and ROM spaces. It

is part of the EEPROM saved setup and is not usually modified during run-time.

HIGH

BYTE

A15

A14

A13

LOW

BYTE

ROM SIZE

RA18

RA17

RA16

RA15

RA14

A15 - A13 and A9 - A5 - These bits are

compared in ISA mode against the I/O address

on the bus to determine the IOBASE for

LAN91C94 registers. The 64k I/O space is fully

decoded by the LAN91C94 down to a 16

location

space,

therefore

the

unspecified

address lines A4, A10, A11 and A12 must be all

zeros.

ROM SIZE - Determines the ROM decode area

in ISA mode memory space as follows:

00 = ROM disable

01 = 16k: RA14-18 define ROM select.

10 = 32k: RA15-18 define ROM select.

11 = 64k: RA16-18 define ROM select.

RA18-RA14 - These bits are compared against

the memory address on the bus to determine

if the ROM is being accessed, as a function of

the ROM SIZE. ROM accesses are read only

memory accesses defined by nMEMRD going

low.

For

full

decode

the

address

space

unspecified upper address lines have to be:

A19 = "1" , A20-A23 lines are not directly

decoded, however ISA systems will only activate

nSMEMRD only when A20-A23=0.

All bits in this register are loaded from the serial

EEPROM.

The I/O base decode defaults to

300h (namely, the high byte defaults to 18h).

ROM SIZE defaults to 01. ROM decode defaults

to CC000 (namely the low byte defaults to 67h).

As an example:

LAN91C94 Datasheet(PDF) 46 Page - SMSC Corporation

LAN91C94 Datasheet(HTML) 46 Page - SMSC Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL