Rom

C H A P T E R 1

Hardware

Figure 1-332-bit and 24-bit memory map comparison

32-bit memory map

24-bit memory map

$FFFF FFFF $FEF0 FFFF

$FE00 0000 $FD00 0000 $FC00 0000

$6000 0000 $5000 0000 $4400 0000 $4000 0000

$0400 0000 $00E0 0000

$0000 0000

Reserved

Slot E (external video)

Reserved

Slot C (internal video)

Reserved

I/O

Reserved

ROM

Expansion RAM

(bus error)

Illegal

RAM

14 MB maximum,

one continuous bank

$FF FFFF $F0 0000

$E0 0000

$D0 0000

$C0 0000

$90 0000

$80 0000

$00 0000

I/O space

Slot E (external video)

Reserved

Slot C (internal video)

Reserved

ROM

RAM

8 MB maximum,

one continuous bank

The Macintosh PowerBook 165c ROM is identical to the ROM used in the PowerBook 160 and PowerBook 180 computers. The ROM chips have been moved from the secondary logic board to a new RAM/ROM board to make room for the color display circuits.

A new 32K x 8-bit declaration ROM appears in NuBus™ slot $C address space and provides ﬁrmware support for the color LCD.

ROM Wait States

ROM accesses by the CPU require 4 processor wait states (7 clock cycles at 33 MHz), which is equivalent to 180 ns per access.

RAM

The PowerBook 165c includes 4 MB of 85 ns pseudostatic RAM, consisting of eight

512K x 8-bit chips. The RAM chips are contained on a new RAM/ROM board to provide room for the color display circuitry on the secondary logic board.

8	Hardware Overview