Specifications

CHAPTER 3
Expansion
30 Expansion Slot
The expansion feature of the Macintosh LC 520 computer is a processor-direct slot that
connects directly to the MC68030 microprocessor. This chapter describes the expansion
slot and gives the specifications for an expansion card.
Expansion Slot 3
The expansion slot in the Macintosh LC 520 computer is an extended processor-direct slot
that accepts either of two types of PDS cards: the 96-pin PDS card used in the
Macintosh LC II computer or the 114-pin PDS card used in the Macintosh LC III. The
114-pin connector provides additional signals to support features of the MC68030
microprocessor that are not available with the 96-pin card.
Note
An expansion card designed for the Macintosh LC II computer will work
in the Macintosh LC 520 computer if the card’s designer has followed the
guidelines in Designing Cards and Drivers for the Macintosh Family, third
edition. ◆
The PDS expansion connector in the Macintosh LC 520 computer is mechanically the
same as the expansion connector in the Macintosh LC III. It is essentially a 120-pin
Euro-DIN connector with six pins removed to make a notch. The notch divides the
connector into two sections: a 96-pin section that accepts the 96-pin connector used
on expansion cards for the Macintosh LC II, and a separate 18-pin section for the
additional signals.
Pin Assignments 3
Pins numbered 1–32 in rows A, B, and C correspond to the 96-pin section of the
connector. Table 3-1 gives the pin assignments for the 96-pin section.
Except for one signal, 16MASTER (on pin B31 and described in Table 3-4), the pin
assignments on the 96-pin section of the extended PDS are the same as those on the PDS
in the Macintosh LC II. On the Macintosh LC II, pin B31 is the Apple II clock input.
Pins 33 and 34 in all three rows are missing—those pins correspond to the notch in the
connector. Pins 35–40 in rows A, B, and C make up the 18-pin section of the extended
connector. Table 3-2 on page 32 gives the pin assignments for the 18-pin section.
Note
Signal names starting with a slash (/) are active when their signal lines
are driven to a logical zero (0).
◆
IMPORTANT
Under no circumstances should you use the Analog GND pin (Pin 1,
Row B) for a digital ground on your expansion card. Doing so will cause
digital noise to be coupled into the audio system, resulting in degraded
sound quality. ▲