Specifications

CHAPTER 2
Hardware Design
Hardware Features 21
Note
The 12” and 7” cards have different BIOS because they have different
microprocessors and chip sets. ◆
At reset, the microprocessor on the card issues the starting reset-vector address from
within the range of addressable memory. The Mustard ASIC remaps this address range
down to the lower 1 MB region where the BIOS actually resides. It also performs the
address translation between the BIOS address on the PC system and the corresponding
addresses in memory on the Macintosh side.
Clock Generation 2
The system clock is generated by a standard oscillator that produces a 14.3 MHz clock
signal. This signal is transferred to a PLL (phased lock loop) device, the IMISC-464 clock
divider, which creates the microprocessor bus clock (66 MHz on the 12” card and 33
MHz on the 7” card), the PCI clock (33 MHz), and the buffered 14.3 MHz clock. Table 2-3
provides information about clock signal distribution.
System Reset 2
The Mustard ASIC contains the reset logic that allows the Macintosh host computer to
start up or reset the PC system. Hard reset is controlled by the Macintosh software. The
Mustard ASIC generates a PWRONRST (power on reset) signal, which, in the 12” card
the 82C557 converts into a Reset signal for the 82C556/558 and the CPU. In the 7” card,
the 85C497 generates reset for the 85C496, the CPU, and the ISA bus. With both cards
you can do a soft reset by means of the Ctl-Alt-Del keys on the PC keyboard. This type of
reset is handled by the 8242 keyboard controller when the proper key code is sent to the
Mustard ASIC through the keyboard port.
Table 2-3 Clock signal distribution
Clock signal Destination Frequency Function
12” card
CPU CLK Microprocessor 66 MHz Provides the bus timing for the microprocessor.
All system timing is referenced from this clock.
7” card
CPU CLK Microprocessor 33 MHz Provides the bus timing for the microprocessor.
All system timing is referenced from this clock.
12” and 7” cards
XPCI CLK ATI-264CT video
controller and
Mustard ASIC
33 MHz Clock for the PCI bus in the PC system.