On Screen Display (OSD) Comparison

Author: Nathaniel W. Crutcher

The following is a brief study of the ICs and modules available for video overlay or on-screen display functionality. This list is by no means complete. If anyone reading this is aware of other good OSD or video overlay ICs, please let me know.

Requirements

• Color NTSC input and output.
• Transparent character background: the original video must be visible behind the characters.
• Easy interface with standard microcontrollers.
• Programmable characters to allow for graphics.
• Wide operating temperature range.

Comparison

STMicroelectronics ST6380, ST6381, ST6382, ST6383, ST6388, ST6389

These are integrated microcontroller / OSD ICs intended for TV on-screen displays. It appears that the actual character set must be pre-specified and mask programmed by STMicroelectronics, so although it may be possible to achieve rudimentary graphics, this would require a high volume of chips to be ordered. The microcontroller core doesn't obviously match any industry standard, so it's not clear whether a C compiler would be available.

STMicroelectronics STV5730

This part is simple and low-cost, but is obsolete.

Decade BOB-3

This is an advanced integrated module that includes video circuitry and a microcontroller. It is controlled via a serial interface and provides 254 ROM characters and 63 user-definable RAM characters. It can display up to 680 characters.

NEC uPD6450, uPD6451A, uPD6453

This appears to be a standard OSD IC for VCRs. The biggest concern with this part is its age (1990) and the fact that it's not clear whether it is being distributed in the United States. I was able to find it listed on a Japanese website, but could not determine its price or availability.

Maxim MAX4455

This is a high-cost IC designed for use with security systems and the like. It can insert OSD into eight video sources. It appears to be designed for grayscale use. It also requires an external video switch to insert the OSD video stream. Although it is grayscale, it does have 15 levels of gray for the OSD overlay.

JRC NJM2252, NJM2262

These are just video overlay ICs that do not generate characters or graphics.

National LM1237, LM1247

These are designed for use in low cost computer monitors. The have mask programmed character sets, support up to four colors, and transparency. The LM1247 support more characters.

National LM1279, LM1281, LM1283

These are just amplifiers that insert an OSD signal into RGB video streams.

Parametric Comparison

This table does not include video overlay ICs that do not generate OSD signals, and it does not include obsolete parts.

• Interface - This lists the native interface for the part. In some cases, additional interface ICs could be used to convert to other interfaces.
  • TV RGB - This refers to a television frequency output, but with separate red, green, and blue channels that would need to be combined into a composite signal.
  • RGB - This device adds the OSD to an arbitrary frequency signal with separate red, green, and blue channels.
  • NTSC - This device adds the OSD to a color NTSC signal.
  • NTSC - This device adds the OSD to a color PAL signal.
  • BW Composite - This device adds the OSD to a black and white composite signal.
  • Composite - This device adds the OSD to a color composite signal.
• Color - This indicates if the OSD can output in more than one color.
• Graphics - This indicates if the OSD has support for user defined characters or graphical output.
  • None - Only displays standard characters and symbols.
  • Chars - Allows custom programmed characters, which can be combined to create simple graphics.
  • Full - Support full bitmapped graphics.
• Transparent - This indicates if the OSD overlay is transparent between the pixels of the characters. Non-transparent OSD creates a solid block in which the characters are displayed through which none of the underlying video can be seen.

¹Rudimentary character based graphics are possible, but would require a custom mask ROM for the character set.

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