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Macintosh Portable PDS Development


The Technical Note describes the unique aspects of the Macintosh Portable Processor Direct Slot (PDS), including the severe limitations in its use.

The internal operating environment of the Macintosh Portable is unique within the Macintosh family due to the additional design goals that are not normally applied to other Macintoshes. In particular, two of these goals which limit the use of the PDS are that the unit shall have a long (eight-hour) battery operation life and that the unit shall meet all FCC regulations, including the ability to operate on commercial aircraft.

[Oct 01 1989]

I've Got a Bad Feeling About This

Because of these design goals and the subsequent limitations on the use of the PDS, you must severely limit your card design for the Macintosh Portable.

The first and foremost limitation is that the PDS has no power budget for your card. Seeing that there are +12V and +5V connections on the PDS connector, we all realize that you could draw some power directly from the Macintosh Portable. Please don't do it. Instead, you should add your own power supply (i.e., battery) to your board, thus controlling your own destiny (or at least the destiny of your PDS board) and ensuring that the Macintosh Portable has the longest battery life of any portable on the market. You are the best judge as to whether or not your board needs to run continuously when the Macintosh Portable is in sleep mode, therefore requiring a long current life. You might find that the functionality of your board is only optimal when the Macintosh Portable is in full-operating mode (or powered by an external source), and in this case, you could conserve its current demands.

For those of you who are convinced that your product is so important that your users will overlook a 50% reduction in their system operating time, Table 1 shows a worst-case power budget that could apply.

  • The 50 mA maximum applies to the loads of the switched and unswitched +5 V supplies.

Table 1-Worst-Case Power Budget

The second limitation is that to meet FCC limits on radio frequency emissions, no connector or cable attached to an expansion card can penetrate the case of the Macintosh Portable.

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So Why Have a PDS Connector at All?

The decision to include the PDS connector is a recognition that we can't know it all. Although it may seem that next to no power availability and absolutely no custom cables to the outside world would block all possible products, providing the expansion connector allows for that spark of genius for which developers are known and the unanticipated product which usually results. So, if after all these dire warnings you still want to proceed, following are the available details (at least until Designing Cards and Drivers for the Macintosh can be updated).

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Hang On

The PDS in the Macintosh Portable provides the microprocessor address, control, data, clock power, and Macintosh Portable-specific lines for your expansion card's use. Table 2 lists these signals, while Table 3 lists their descriptions.

Table 2-Macintosh Portable 68000 Direct Slot Expansion Connector Pinouts

Table 3-Functional Description of the Macintosh Portable PDS Signals

The signals listed in Tables 2 and 3 are presented to your PDS card through a Euro-DIN 96-pin socket connector on the main logic board.

Currently, you can order these Euro-DIN 96-pin connectors (which meet Apple specifications) from: AMP Incorporated, Harrisburg, PA 17105.

Disclaimer: This listing for AMP Incorporated neither implies nor constitutes an endorsement by Apple Computer, Inc. If your company supplies these connectors and you would like to be listed, contact DTS at the address in Technical Note #0.

Figure 1-96-Pin Plug Connector

Due to the limited space within the Macintosh Portable's case, your card is limited to the size indicated in Figure 2. Apple highly recommends the use of CMOS circuits to reduce the total power necessary for your card's operation.

Figure 2-PDS Expansion Card Dimensions

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Designing Cards and Drivers for the Macintosh

Guide to the Macintosh Family Hardware

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Acrobat gif

Acrobat version of this Note (472K)


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