Specifications

CHAPTER 3
Expansion
34 The PDS Expansion Card
▲
WARNING
The SNDOUT pin must not be grounded; doing so will short-circuit the
+5V power to the sound ciruitry. If you don’t use the SNDOUT pin, leave
it unconnected. ▲
The PDS Expansion Card 3
The PDS expansion card for the Macintosh LC 520 computer is approximately 3 inches
wide by 5 inches long. It mounts parallel to the main logic board and reaches to an
opening in the back of the case (normally filled by a snap-out cover). The opening
provides access to a 15-pin D-type connector on the card for external I/O.
The PDS card for the Macintosh LC 520 computer is the same size and shape as the PDS
card for the Macintosh LC III computer. The section “Foldouts” at the end of this
developer note contains mechanical drawings showing the recommended design
guidelines for the PDS card. Foldout 1 shows the maximum dimensions of the expansion
card and the location of the PDS connector. Foldout 2 provides component height
/FPU.SEL Select signal for an optional MC68881 or MC68882 FPU on the card.
/PDS.AS Address strobe synchronized to 16 MHz regardless of the actual processor speed;
used to indicate the occurrence of an active bus transaction. /PDS.AS is asserted
only when a valid slot address is being generated by the bus master or by an access
to the FPU. Slot addresses are in the slot $E range ($xxExxxxx in 24-bit mode,
$FExxxxxx or $Exxxxxxx in 32-bit mode). When a PDS card is the active bus master,
the card may drive either /PDS.AS or /CPU.AS, but not both.
/PDS.DSACK0,
/PDS.DSACK1
Data transfer acknowledge signals from the PDS card.
16MASTER Indicates the width of the data port when the card is alternate bus master. A logical
one (1) indicates a 16-bit port; logical zero (0) indicates a 32-bit port. The signal is
pulled high on the main logic board.
/SLOT.BG Bus grant signal to the expansion card. A bus master card may take control of the
system bus after all pending bus traffic has been completed (when /PDS.AS,
/BGACK, and all /DSACK signals are inactive).
/SLOTIRQ Interrupt request line from the card; reported to the system by way of the SLOT.E
request; when low, generates a level-2 interrupt if the slot interrupt enable bit is set.
/SLOTIRQ.C,
/SLOTIRQ.D
For future expansion; not used in the Macintosh LC 520 computer.
SNDOUT Input to the speaker amplifier so that the card can drive the speaker independently
of the main processor. This signal accepts only sound output by the method used
on the original Apple II, using 1’s and 0’s.
Table 3-4 Expansion slot signals not connected to the MC68030 (continued)
Signal name Signal description