Compaq 850 manual Rambus Attributes, Rambus Signal Attributes Each Channel, Signal Name

Chapter 3 Processor/Memory Subsystem

3.3.1 RAMBUS ATTRIBUTES

To ensure signal quality during high-speed memory transfers, the Rambus interface design departs from previous memory interface designs in several key aspects (Figure 3-4). Rambus uses a daisy- chained signal distribution system that requires that all memory sockets be populated with either a RIMM or a continuity module (CRIMM) in order to maintain constant load impedance. Rambus Signaling Levels (RSL) uses a 1.4-volt reference with a 0.8-volt swing between logic 0 at 1.8 V and logic 1 at 1.0 V.

On these systems RIMMs (or CRIMMs) must be installed in pairs (one module for each channel). A maximum of two gigabytes of memory may be installed using 512-MB RIMMs. These systems ship with PC800 (400-MHz) RIMMs but will also accept PC700 or PC600 RIMMs. A mix of ECC and non-ECC RIMMs may be installed, although all RIMMs must be ECC to realize ECC benefits.

						RIMM or CRIMM (Shown)
			RIMM
						RIMM
MCH	Channel 1
		Channel 2				Bus Termination
				RIMM Sockets
			Rambus Signal Attributes (Each Channel)
	No. of		Input/	Signal
Signal Name	Lines		Output [1]	Level	Impedance	Function
ROW 2..0	3		O	RSL	28 ohms	Row address
COL 4..0	5		O	RSL	28 ohms	Column address
DQA 8..0	9		I/O	RSL	28 ohms	Data byte A (w/parity or ECC bit)
DQB 8..0	9		I/O	RSL	28 ohms	Data byte B (w/parity or ECC bit)
CFM, CFMN	2		O	RSL [2]	28 ohms	400-MHz Clock-from-master for writes
CTM, CTMN	2		I	RSL [2]	28 ohms	400-MHz Clock-to-master for reads
Vref	1		--	1.4 V	--	Reference voltage for RSL signals
SIO	1		I/O	CMOS	--	Serial I/F for initialization & pwr cntrl.
SCK	1		O	CMOS	56 ohms	SIO clock; 1 MHz for configuration,100
						MHz for power management.
CMD	1		I/O	CMOS	56 ohms	Serial I/F config. & power control
Vdd			--	2.5 V	--	Power for Rambus circuitry

NOTES:

[1]Relative to the memory controller.

[2]Differential pair with Ep-p swing of 400 to 600 mV.

Figure 3–4.Rambus Channel Signal Distribution and Key Attributes

3-6Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition - December 2000