MAX4455EVSYS データシートの表示（PDF） - Maxim Integrated

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MAX4455EVSYS

MAX4455 Evaluation Kit/Evaluation System

Maxim Integrated 

MAX4455 Evaluation Kit/Evaluation System

Character Generator

The MAX4455 EV kit software can generate text labels

using any standard Windows font installed on the host

computer system. Typical Windows systems usually

include Arial, Courier New, and Times New Roman

fonts.

The font selector button runs the standard Windows

font selector dialog box, which lets you choose from

any of the fonts installed on your system.

The text color buttons set the text foreground color to

luma values of 100 IRE, 74 IRE, 47 IRE, or 0 IRE.

Detailed Description

of Hardware

The MAX4455 EV kit consists of a MAX4455 arbitrary

graphics on-screen display video generator, a

synchronous dynamic RAM, a 3.3V crystal oscillator

module, and a 3.3V linear regulator. Cost-sensitive

applications can replace the crystal oscillator module

with a 40.5MHz fundamental mode crystal. Resistor R1

sets the white video fill. (Refer to the MAX4455 data

sheet for white level calculation.)

The crosspoint outputs are sampled through the right-

angle connector J5, or can optionally be fed through

the BNC jacks. Resistor/capacitor networks such as

C32-C33-R10 sample the video signals.

Because the MAX4455 EV system uses a bidirectional

parallel printer cable as opposed to a local microproces-

sor bus, Schmitt triggers are used to sharpen the rise

times of the read and write strobes. These Schmitt trigger

buffers are located on the MAX4358 EV kit companion

board.

Design Considerations

For best picture quality, the design of a custom

MAX4455 on-screen display system requires careful

attention to the ground return paths. The MAX4455

video outputs switch a significant amount of current into

the analog ground return.

The EV kit is designed as a two-board set to accommo-

date customers using different video crosspoints.

However, for best results, the MAX4455 should be

located close to the crosspoint switch.

The MAX4455 is designed to interface directly to a

microprocessor. The EV kit uses the parallel port for

ease of evaluation, which is not recommended for pro-

duction designs. Throughput is severely limited, and

the long cable requires Schmitt trigger buffers to clean

up the read/write strobes.

Troubleshooting

Problem: display seems to flicker

Interlaced raster scan can appear to flicker for test patterns

that have sharp, single-pixel horizontal lines. Flicker is worst

on small, bright, high-contrast features. Apply a digital anti-

aliasing function across the test pattern before writing it to

the MAX4455. Do not write single-pixel lines; instead, write

both field 1 and field 2 of each NTSC line pair.

Problem: software can’t read MAX4455 EV kit

Although the MAX4455 EV kit works directly with most

modern computers, some systems require that the paral-

lel port must be enabled for bidirectional mode in the

BIOS setup screen. You must reboot your computer,

enter BIOS setup before Windows starts, find the integrat-

ed peripherals screen, and ensure that the LPT port is

configured as an ECP port. Standard and EPP parallel

port settings are not compatible with the MAX4455 EV kit.

Problem: switching channels causes the display to roll

If the MAX4455 inserts video fill during the vertical blank-

ing interval, it can miss the vertical sync information. The

solution is to set the BLANK bit true when switching the

crosspoint. Once video sync is established, set the

BLANK bit false to re-enable the video fill. (Refer to the

MAX4455 data sheet for more information.)

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