HP P Class 450/500/550/600/650/700/750 Reference Manual page 43

System Board
Chipset
IDE Controller
The PCI master/slave IDE controller (Bus Master capability and synchronous DMA mode),
supporting four devices, two on each of the two channels, is described in the section
"Devices on the PCI Bus" in this chapter.
Enhanced USB Controller
The USB (Universal Serial Bus) controller provides support for the Universal Host
Controller Interface (UHCI). This includes support that allows legacy software to use a
USB-based keyboard and mouse. The USB supports two stacked connectors on the back
panel. These ports are built into the PIIX4E controller, as standard USB ports. The USB is
described in detail in the section "Universal Serial Bus (USB) Controller" in this chapter.
Ultra DMA Controller
The seven-channel DMA controller incorporates the functionality of two 82C37 DMA
controllers. Channels 0 to 3 are for 8-bit DMA devices, while channels 5 to 7 are for 16-bit
devices (refer to the section "DMA Channel Controllers" in the chapter "HP BIOS"). The
channels can be programmed for any of the four transfer modes: the three active modes
(single, demand, block) can perform three different types of transfer: read, write and verify.
The address generation circuitry supports a 24-bit address for DMA devices.
Interrupt Controller
Based on two 82C59 interrupt controllers. The two interrupt controllers are cascaded so
that 14 external and two internal interrupts are possible. In addition, PIIX4E supports a
serial interrupt scheme. It also supports the onboard I/O APIC controller 82093AA. A table
in the section "Interrupt Controllers" in the chapter "HP BIOS" shows how the master and
slave controllers are connected.
Counter / Timer
The chip contains a three-channel 82C54 counter/timer. Three counters are combined to
provide the system timer function, refresh request, and speaker tone. The counters use a
division of the 14.318 MHz OSC input as the clock source.
Serial EEPROM
This is the non-volatile memory which holds the values for the Setup program (they are no
longer stored in the CMOS memory). The Serial EEPROM is described in the section
"Serial EEPROM" in this chapter.
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