Address Multiplexing

Signals A[0] - A[12] and BA[0] - BA[1] on each RAM SO-DIMM make up a 15-bit multiplexed address bus that can support several different types of SDRAM devices. Table 4-2 lists the types of devices that can be used in the PowerBook G4 computer by size, configuration, and sizes of row, column, and bank addresses.

Expansion Features

Important

The PowerBook G4 computer supports only the types of SDRAM devices specified in Table 4-2. Other types of devices should not be used with this computer.

Table 4-2 Types of DRAM devices

Device size

Device configuration (bytes x bits banks)

Row address bits

Column address bits

64 Mbits

2 M x 8 x 4

12

9

64 Mbits

1 M x 16 x 4

12

8

64 Mbits

512 K x 32 x 4

11

8

128 Mbits

4 M x 8 x 4

12

10

128 Mbits

2 M x 16 x 4

12

9

128 Mbits

1 M x 32 x 4

12

8

256 Mbits

8 M x 8 x 4

13

10

256 Mbits

4 M x 16 x 4

13

9

RAM SO-DIMM Electrical Limits

Each RAM SO-DIMM must not exceed the following maximum current limits on the +3.3 V supply:

Active: 1.2 A (8 devices at 150 mA each)

Sleep: 12 mA

Important

The restriction on sleep current is required not only to maximize the battery life but to meet the limitations of the backup battery during sleep swapping of the main battery. Developers of RAM expansion modules that exceed the limit on sleep current must include a warning to the user that battery sleep swapping may not work with those modules installed.

The maximum current specified for active operation generally rules out the use of 4-bit-wide SDRAM devices in a RAM expansion module. Such a module would have 16 such devices, and the 1.2 A maximum current would allow only about 75 mA per device. To stay within the current limits, RAM expansion modules should use only 8-bit or 16-bit SDRAM devices.

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