Motherboard Design - Computer Busses - page 129

DMA channels, and distribute DMA which is based on monitoring CPU accesses to the 8237
controller (this was not implemented on the PIIX3).
The PIIX4 also supports Ultra DMA/33 Synchronous DMA mode transfers up to
33MB/s. Ultra DMA is a newer protocol for the IDE hard drive interface that doubles the
burst data rate from 16.6 MB/s (as supported by the PIIX3). Ultra DMA widens the path to
the hard drive by transferring twice as much data per clock cycle, so doubling the perform-
ance. The Ultra DMA protocol lets host computers send and receive data faster, removing
bottlenecks associated with data transfers.
In addition to speed improvements, the protocol brings new data integrity capabilities to
the IDE interface such as improved timing margins and data protection verification. Ultra
DMA protocol also allows drives and system to retain backward compatibility with the pre-
vious ATA standard.
Real time clock
The real-time clock provides a data-and-time keeping device with alarm features and battery-
backed operation. The RTC counts seconds, minutes, hours, days, day of the week, date,
month and year. It counts 256 bytes of battery-backed SRAM in two banks. The RTC mod-
ule requires an external oscillator source of 32.768 kHz connected between TXCX1 and
RTCX2.
5.2.2 I/O controller
The PC87306B I/O controller is similar to the 82091AA (AIP) used in the 430HX board. It
has:
• Floppy disk interface - provides support for several different floppy disk capacities and
sizes.
• Multimode parallel port - supports for output only compatibility mode, bidirectional
mode, EPP mode and ECP mode.
• Two FIFO serial ports. Giving transfers rates up to 921Kbps.
• Real-time clock - provides time-of-day, 100-year calendar and alarm features.
• Keyboard and mouse controller - keyboard and mouse interfaces (as well as power
on/reset password protection).
• Infrared support - connection to infrared transmitter/receiver.
5.2.3 Graphics subsystem
The 430HX incorporates the ATI-241 Rage II+ graphics controller which has:
• Drawing coprocessor that operates concurrently with the host processor.
• Video coprocessor.
• Video scalar, colour space converter, true colour palette.
• ATI multimedia.
• Enhanced power features.
• VGA/VESA capability.
The 430HX also has an optional video capture processor for digitising analogue inputs from