DP83905AVQB datasheet(9/80 Pages) NSC

9 / 80 page

40 Functional Description (Continued)

TLF11498 – 4

FIGURE 1 Block Diagram of ATLANTIC Controller

DETERMINING 8- OR 16-BIT WIDE DATA

ATLANTIC Controller can treat the system data bus and all

internal data busses as 8 or 16 bits wide 8- or 16-bit mode

is determined by the DWlD pin For an adapter card this bit

can be used to automatically detect if the card has been

plugged into an 8- or 16-bit slot If this pin is connected to a

VDD on the upper connector it will be high when plugged

into a 16-bit slot enabling 16-bit mode and floating when

plugged into an 8-bit slot When floating the internal pull-

down resistor will enable 8-bit mode

SHARED MEMORY ARCHITECTURE

TLF11498 – 5

FIGURE 2 Shared Memory

In this mode the ATLANTIC Controller’s internal memory

map using external RAM devices is mapped into the host

system’s memory map Both the ATLANTIC Controller and

the host system can directly access this memory The

ATLANTIC Controller controls the arbitration for this mem-

ory area giving priority to its internal accesses It also has

an internal FIFO to allow for any latency on internal trans-

fers introduced by system accesses If a system access oc-

curs while an internal access is current the ATLANTIC

Controller will insert wait states into the system cycle until

the internal transfer is complete

In this mode the ATLANTIC Controller’s internal registers

are accessed within the system’s IO map The address

within this IO map is set by Configuration Register A The

user programs the address of the shared memory within the

host systems memory map by writing to a register in

ATLANTIC Controller The memory is not accessible by

the user until after this register has been programmed

There are two basic Shared Memory modes compatible

mode and non-compatible mode as described in the fol-

lowing text

DP83905AVQB Datasheet(PDF) 9 Page - National Semiconductor (TI)