DP83905AVQB datasheet(12/80 Pages) NSC

12 / 80 page

40 Functional Description (Continued)

line ATLANTIC Controller will not begin the next memory

read until the previous word of data has been read

On a remote write the system writes data to the IO port

using

‘‘OUTW’’

‘‘OUTSW’’

instruction

and

ATLANTIC Controller moves it to its buffer memory If the

system attempts to write to the port before ATLANTIC

Controller has moved the data to memory ATLANTIC Con-

troller will insert wait states into the system cycle using the

CHRDY line ATLANTIC Controller will not begin the next

memory write until a new word has been written to the IO

port

Addresses 00H to 1FH are specified as the PROM space

for compatibility with the NE2000 This is actually an array of

8-bit registers which are loaded from an external EEPROM

after ATLANTIC Controller is initialized by an ISA RESET

They should contain the same data as the PROM did in the

NE2000 and in the same format As can be seen the PROM

registers are only 8-bits wide To transfer the data out the

user must initiate a 16-bit DMA read transfer and discard the

most significant byte of data on each transfer

At address 00H of the PROM is a six byte Ethernet address

for this node The upper two addresses of the PROM store

contain bytes which identify whether the ATLANTIC Con-

troller is in 8- or 16-bit mode For 16-bit mode these bytes

both contain the value 57H for 8-bit mode they both contain

42H

8-BIT IO PORT COMPATIBLE MODE

This mode is compatible with the 8-bit mode offered by

Novell’s NE2000 The NE2000 automatically detects wheth-

er it is in an 8- or 16-bit slot and configures itself appropri-

ately As explained in the previous paragraphs the user can

determine whether the board is in 8- or 16-bit mode by read-

ing the PROM In 8-bit mode only 8 kbytes of RAM are

addressable as in the 8-bit mode of the NE2000 The IO

map is the same as the 16-bit mode the memory map is

shown in

Figure 7 Again the PROM has only a partial de-

code so is mirrored at all addresses up to 4000H The

PROM still occupies 32 bytes of address space although it

only has 16 bytes of data as the data at all odd address

locations is merely a mirror of the data at the previous even

address location The RAM is mirrored at 6000H and the

entire map mirrored at 8000H

A low cost card using only one 8 kbyte RAM can be de-

signed If the DWlD pin is left unconnected or tied to GND

then the ATLANTIC Controller will always operate in 8-bit

mode regardless of the slot the board is in

IO PORT NON-COMPATIBLE MODE

This mode is similar to Novell’s NE2000 but this mode al-

lows the user to use the full 64 kbytes of address space

except for an initial page for the PROM The memory map

for this board is shown in

Figure 8 The memory map is the

same for both 8- and 16-bit modes Although the PROM

store occupies 256 bytes it is only 16 bytes long The entire

map is mirrored at 8000H

A low cost card using only one 8 kbyte RAM can be de-

signed If the DWID pin is left unconnected or tied to GND

then the ATLANTIC Controller will always operate in 8-bit

mode regardless of the slot the board is in

0000h

0020h

PROM

Aliased PROM

4000h

8k x 8 BUFFER RAM

6000h

RESERVED

8000h

(a)

D15

1EH

42H

1CH

42H

RESERVED

0AH

E’net Address 5

08H

E’net Address 4

06H

E’net Address 3

04H

E’net Address 2

02H

E’net Address 1

00H

E’net Address 0

(b)

FIGURE 7 a) 8-Bit NIC Core’s Memory Map

b) 8-Bit PROM Map

0000H

00FFH

PROM

0100H

BUFFER RAM

FFFFH

FIGURE 8 IO Port Enhanced Mode

DP8390 Core Memory Map

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