Technical information

CHAPTER 2
Hardware Design
PDS Adapter Card 29
Autoconfiguration 2
The Pretzel Logic IC performs autoconfiguration each time the PC is reset. The following
configurations are sensed and set upon reset:
■ Presence of local DRAM (SIMM installed on the card)
■ Video monitor adapter cable installed on the Macintosh computer (this cable must be
installed to share a single monitor between the host computer and the card)
■ PDS card ID (000)
The video monitor adapter cable must be installed to share a single monitor between
the Macintosh host computer and the card. The PDS card ID for the DOS Compatibility
Card is 000.
Declaration ROM 2
For the onboard declaration ROM, the Pretzel Logic IC provides decoding of slot $E
addresses in the $FEXX XXXX range. The device used for the declaration ROM is a 32 KB
ROM IC with an access time of 150 ns.
PDS Adapter Card 2
The PDS adapter card is the interface between the processor card and the processor-
direct slot in the Power Macintosh 6100. It contains the bus demultiplexer buffers and
the AJA custom IC that controls them.
AJA Bus Controller IC 2
The control logic for the interface between the Pretzel Logic IC’s 68040 bus and the host
computer’s PowerPC 601 bus is implemented in a custom gate array called the AJA IC.
The AJA IC controls the bus demultiplexing and translates the PDS control signals from
the Macintosh computer.
The AJA IC provides the following functions:
■ selection of upper or lower longword on the bus
■ control of bus buffer direction
■ control of bus grant to allow for retry
■ bus arbitration to avoid preemption