Dual Video/Memory Clock Generator

Integrated

Circuit

Systems, Inc.

ICS2495

Notes:

1. ICS2495M(SOIC) pinout is identical to ICS2495N(DIP).

Pin Configuration

XTAL2

1

16

XTAL1

EXTFREQ

2

15

VCLK

FS0

3

14

XTALOUT

FS1

4

13

VSS

STROBE

5

12

VDD

FS2

6

11

N/C

FS3

7

10

MCLK

MS0

8

9

MS1

16-Pin DIP or SOIC

Features

•• Low cost - eliminates need for multiple crystal clock

oscillators in video display subsystems

•• Mask-programmable frequencies

•• Pre-programmed versions for Industry Standard VGA

chips

•• Glitch-free frequency transitions

•• Internal clock remains locked when the external frequency

input is selected

•• Low power CMOS device technology

•• Small footprint - 16-pin DIP or SOIC

•• Buffered Xtal Out

•• Integral Loop Filter components

•• Fast acquisition of selected frequencies, strobed or non-

strobed

•• Guaranteed performance up to 135 MHz

•• Excellent power supply rejection

•• Advanced PLL for low phase-jitter

•• Frequency change detection circuitry enhances new fre-

quency acquisition and eliminates problems caused by

programs that rewrite frequency information

Description

The ICS2495 Clock Generator is an integrated circuit dual

phase-locked loop frequency synthesizer capable of generating

16 video frequencies and 4 memory clock frequencies for use

with high performance video display systems. Utilizing CMOS

technology to implement all linear, digital and memory func-

tions, the ICS2495 provides a low-power, small-footprint,

low-cost solution to the generation of video dot clocks. Outputs

are compatible with XGA, VGA, EGA, MCGA, CGA, MDA,

as well as the higher frequencies needed for advanced applica-

tions in desktop publishing and workstation graphics. Provi-

sion is made via a single level custom mask to implement

customer specific frequency sets. Phase-locked loop circuitry

permits rapid glitch-free transitions between clock frequencies.

In addition to providing 16 clock rates, the ICS2495 has

provisions to multiplex an externally-generated signal source

into the VCLK signal path. Internal phase-locked frequencies

continue to remain locked at their preset values when this mode

is selected. This feature permits instantaneous transition from

an external frequency to an internally-generated frequency.

Printed circuit board testing is simplified by the use of these modes

as an external clock generated by the ATE tester can be fed

through, permitting synchronous testing of the entire system.

ICS2595RevA090694