DP83905 datasheet(13/80 Pages) NSC

13 / 80 page

40 Functional Description (Continued)

42 POWER ON RESET OPERATION

The ATLANTIC Controller configures itself after a Reset

signal is applied To be recognized as a valid Power-On-Re-

set the Reset signal must be active for at least 415 ms

Figure 9 shows how the RESET circuitry operates

TLF11498 – 7

FIGURE 9 RESET Operation

The ISA standard determines that within 500 ns of RESET

going active all devices should enter the appropriate reset

condition The ATLANTIC Controller will generate the inter-

nal signal IOinactive after RESET has been active for

415 ns which will disable all outputs and cause RESET to

be the only input monitored The ATLANTIC Controller will

not respond to a RESET pulse of shorter duration than this

An internal timer continues to monitor the amount of time

RESET is active After 415 ms it is considered a valid Power-

On-Reset and an internal signal called RegLoad is generat-

When a Power-On-Reset occurs the ATLANTIC Controller

latches in the values on the configuration pins and uses

these to configure the internal registers and options Inter-

nally these pins contain pull-down resistors which are en-

abled when IOinactive goes active If any pins are uncon-

nected they default to a logic zero The internal pull-down

resistor has a high resistance to allow the external pull-up

resistors to be of a high value This limits the current taken

by the memory support bus The suggested external resistor

value is 10 kX The configuration registers are loaded from

the memory support bus when RESET goes inactive if Reg-

Load is active The internal pull-down resistors are enabled

onto the bus until RegLoad has gone inactive

A Power-On-Reset also causes the ATLANTIC Controller

to load the internal PROM store from the EEPROM which

can take up to 320 ms This occurs after RegLoad has gone

inactive The ATLANTIC Controller will be inaccessible dur-

ing this time If EECONFIG is held high the configuration

data loaded on the falling edge of RESET will be overwritten

with data read from the serial EEPROM Regardless of the

level on EECONFIG the PROM store will always be loaded

with data from the serial EEPROM during the time specified

as EELoad

43 EEPROM OPERATION

The

ATLANTIC

Controller

uses

NM93C06

EEPROM with compatible timings The NM93C06 is a 256-

bit device arranged as 16 words each 16 bits wide The

programmed contents of the EEPROM is shown in

Figure

Mapping EEPROM Into PROM Space

Data is read from the EEPROM at boot time and stored in

registers within the ATLANTIC Controller While this opera-

tion takes place the ATLANTIC Controller can not be ac-

D15

0FH

73H

Config C

0EH

Config B

Config A

08H

42H

07H

57H

03H

Reserved

(Checksum)

(Board Type)

02H E’net Address 5 E’net Address 4

01H E’net Address 3 E’net Address 2

00H E’net Address 1 E’net Address 0

Note 1

The contents of locations 03H and 04H differ between IO Mode

and Shared Memory Mode The Shared Memory Mode values are shown in

parentheses For compatibility with both modes default to the shared memo-

ry mode values

Note 2

Programming 73H into the upper address is not absolutely required

but is strongly recommended for future compatibility of manufacturing pro-

cess

FIGURE 10 EEPROM Programming Map

cessed by the system These registers are mapped into the

space traditionally occupied by the PROM in the NE2000 or

the EtherCard PLUS16 The size and format of this data

read is determined by the mode of operation

SHARED MEMORY MODE

In this mode program the EEPROM to contain the node’s

Ethernet address in the first six bytes a byte identifying the

type of board ATLANTIC Controller is emulating in byte 7

and a checksum byte in byte 8 The two’s complement sum

of these eight bytes should equal FFH

In this Mode the ATLANTIC Controller reads the first 4

words from the EEPROM and maps them into the IO map

at the appropriate address

IO PORT MODE

In this mode program the EEPROM to contain the node’s

Ethernet address in the first six bytes The user should then

program 5757H and 4242H into the subsequent bytes The

ATLANTIC Controller will decide which of these values

should be loaded into the PROM store depending on the

DWlD pin (The data width is programmed in this mode by

setting the WTS bit in the Data Configuration Register and

setting the DWlD pin for the proper mode) If some other

numerical values are preferred to indicate the mode then

they can be programmed at this location in the EEPROM

and ATLANTIC Controller will put them at the correct ad-

dress

In this mode the ATLANTIC Controller reads the first 7

words from the EEPROM and maps them into the memory

map at the appropriate address If in 16-bit mode it also

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