FAIRCHILD AN-5005 Data Sheet

-5005 P 100 M em ry D river C etitive C ariso

AN-5005 Fairchild Semiconductor Application Note March 1999 Revised December 2000

PC100 Memory Driver Competitive Comparisons Introduction Overview The latest developments in chipset and motherboard Fairchild Semiconductor’s CROSSVOLT VCX family design have taken memory performance requirements to offers a variety of logic solutions that meet or exceed the new levels. The memory bus speed has been increased PC100 specification. from 66MHz to 100MHz to keep pace with the needs of

Device # Function

advanced operating systems and software. Feeding today’s PC/workstation/server often requires large banks of 74VCX16835 18 Bit Universal Buffer dense SDRAM (Synchronous DRAM) ICs arranged on

74VCX162835 18 Bit Universal Buffer

DIMMs (Dual in-line memory modules). Due to the inability

w/ 25 Ω Resistor

of the system memory controller to drive the large amount

74VCX16838 16 Bit Selectable Register Buffer

of memory devices and maintain signal integrity or system

timing requirements, many of today's DIMMs require buff- 74VCX162838 16 Bit Selectable Register Buffer

w/ 25 Ω Resistor

ering of the address and control signal paths. Intel has pub- lished a specification for 100MHz SDRAM memory 74VCX16839 20 Bit Selectable Register Buffer modules called PC100. Proper selection of the logic

74VCX162839 20 Bit Selectable Register Buffer

devices to register and redrive heavily loaded address and

w/ 25 Ω Resistor

control signal paths requires careful consideration of

The information in this application note provides functional

device parameters and can result in a SDRAM DIMM

and specification comparisons to several ALVC devices

design that uses the fewest components and provides reli-

that are also used in DIMM applications. There are several

able circuit performance (Note 1). This application note

device number differences between the two families. The

compares Fairchild Semiconductor’s logic solutions for

table below provides a cross reference between VCX and

buffered (or registered) DIMMs to other competitive solu-

ALVC.

tions. Note 1: See Fairchild Semiconductor AN-5003 PC100 SDRAM Memory Driver Solutions

VCX and ALVC Cross Reference Table

Fairchild Device # ALVC Device # Function 74VCX16835 74ALVC16835 18 Bit Universal Buffer 74VCX162835 74ALVC162835 18 Bit Universal Buffer w/ 25 Ω Resistor 74VCX16838 74ALVC16334 16 Bit Selectable Register Buffer 74VCX162838 74ALVC162334 16 Bit Selectable Register Buffer w/ 25 Ω Resistor 74VCX16839 74ALVC16836 20 Bit Selectable Register Buffer 74VCX162839 74ALVC162836 20 Bit Selectable Register Buffer w/ 25 Ω Resistor

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