HP Vectra VL800, Technical Reference Manual

Page: 55 / 147

55
3 System Board
Memory Controller Hub (82850)
The AGP bus is based upon a 66 MHz, 32-bit PCI bus architecture, to which
several signal groups have been added to provide AGP-specific control and
transfer mechanisms.
AGP specific transactions always use pipelining. This control mechanism
increases the bus efficiency for data transfer. Sideband Addressing (SBA)
may also be used by AGP transaction requests which further increases the
bus efficiency for data transfer. The supported modes are detailed below:
• FRAME-based AGP. Only the PCI semantics are: 66 MHz, 32-bit, 1.5 V,
266 MB/s peak transfer rate.
• AGP 1X with pipelining, sideband addressing can be added: uses 66 MHz,
32-bit, 1.5 V, increased bus efficiency, 266 MB/s peak transfer rate.
• AGP 2X with pipelining, sideband addressing can be added: 66 MHz
double clocked, 32-bit, 1.5 V, 533 MB/s peak transfer rate.
• AGP 4X with pipelining, sideband addressing can be added: 133 MHz
double clocked, 32-bit, 1.5 V, increased bus efficiency, 1066 MB/s peak
transfer rate
AGP PCI Bus
Implementation
Main Memory Controller
The main memory controller is integrated in the MCH supporting two
primary rambus channels (A and B).
Pentium 4 Processor
GX-Device 1
AGP Port
Interface
PCI-to-PCI
Device 0
I850
Memory
Controller Hub
(MCH)
1.5V
AGP
Connector
AGP 4x Bus
(133 MHz)
Hub Link 8-bit
I/O Controller
Hub (ICH2)