Apple II Computer Info
issues for doing DMA on the IIgs which can cause compatibility problems.
Pin 23: this is used for the interrupt daisy chain (out) on all slots
except 7. In the IIe only, this pin can be connected to the GR signal
(graphics mode enabled) via a motherboard modificatoin.
Pin 24: DMA daisy chain out.
Pin 25: +5V.
Pin 26: Ground.
Pin 27: DMA daisy chain in.
Pin 28: Interrupt daisy chain in.
Pin 29: Non Maskable Interrupt.
Pin 30: Interrupt Request.
Pin 31: Reset.
Pin 32: this is the INHIBIT pin on all machines. This behaves
differently on all three machines: the II and II+ only allow the
$D000-$FFFF ROM area to be inhibited. The IIe allows RAM to be
inhibited as well, but has strange interaction with main and auxiliary
memory. The IIgs only allows this signal to be used if the machine is
running in slow mode.
Pin 33: -12V.
Pin 34: -5V.
Pin 35: unused on the II and II+. On the IIe and IIgs, this is the
colour reference signal on slot 7 only. It is unused for other slots
in the IIe, except for slot 1 where it provides a poorly documented
facility to disable the keyboard address decoding. On the original
IIgs, slot 3 provides the M2B0 signal (Mega II Bank 0) via this pin and
it is unused on other slots. The ROM 3 provides M2B0 for slots 1 to 6.
Pin 36: 7 MHz system clock.
Pin 37: Q3 - Asymmetrical 2 MHz clock.
Pin 38: Phase 1 clock (1.023 MHz).
Pin 39: something called "USER 1" on the II and II+, which can be used
to disable all I/O decoding if a modification is made on the
motherboard. On the IIe, this pin provides the SYNC signal from the
micro, which indicates an opcode fetch. On the IIgs, this pin
provides the M2SEL signal, which indicates that a valid slow memory
access is in progress. This pin must be used by IIgs cards that
decode the address without use of the IOSEL, IOSTRB or DEVSEL pins.
Pin 40: Phase 0 clock (1.023 MHz).
Pin 41: Device Select ($C0n0-$C0nF, where n is the slot number plus 8).
Pins 42-49: Data bus.
Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 42 of 572
(22 pages)
(16 pages)
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