HP Integrity rx8620 Server User Service Guide

in the system. It connects to the processor dependent hardware (PDH) and micro controller
hardware. Each cell board holds up to 16 DIMMS. Between one to four cell boards can be installed
in the server. A cell board can be selectively powered off for cell replacement without affecting
cells in other configured partitions.
Figure 1-5 Cell Board
The server has a 48 V distributed power system and receives the 48 V power from the system
backplane board. The cell board contains DC-to-DC converters to generate the required voltage
rails. The DC-to-DC converters on the cell board do not provide N+1 redundancy.
The cell board contains several major buses including:
• Front side buses (FSB) for each of the four processors
• Two memory buses (one going to each half of the main memory array)
• Incoming and outgoing I/O bus that goes off board to a SBA chip
• Incoming and outgoing crossbar bus that goes off board to the other cell board
• PDH bus that goes to the PDH and micro controller circuitry
All of these buses come together at the CC chip.
Because of space limitations on the cell board, the PDH and micro controller circuitry reside on
a riser board that plugs at a right angle into the cell board. The cell board also includes clock
circuits, test circuits, and de-coupling capacitors.
Figure 1-6 shows a simplified view of the memory subsystem. It consists of two independent
access paths, each path having its own address bus, control bus, data bus, and DIMMs . In practice,
the CC runs the two paths 180 degrees out of phase with respect to each other to facilitate
pipelining in the CC. Address and control signals are fanned out through register ports to the
synchronous dynamic random access memory (SDRAM) on the DIMMs.
The memory subsystem is composed of four independent quadrants. Each quadrant has its own
memory data bus connecting from the cell controller to the two buffers for the memory quadrant.
Each quadrant also has two memory control buses; one for each buffer.
HP Integrity rx8620 Server Block Diagram 21