A simple SCART interface for video

By Bill Stutz and Miles Bekgran
Maxim Integrated Products Inc.

In Europe, all external connections to video peripherals such as TVs, STBs and VCRs are provided by a SCART (Peritel) connector, with pin-out as specified in the EN50049 standard. Depending on the SCART connector's use (TV SCART, AUX SCART, or VCR SCART) the connector is an input, an output, or both. The addition of S-VHS has complicated this interface by requiring the RED and Cvbs signals (pins 15 & 20) to be shared with the Chroma (C) and Luma (Y) pins.

In most cases, specialized ICs are used for the SCART Interface because of the complicated switching required, but that approach isn't cost effective for smaller unidirectional implementations. (The simplest form is the single SCART switch found on TV inputs and encoder outputs.) An alternative method (Fig. 1 to 3) provides a high-quality interface without the need to add switches or a multiplexer.

In these figures, the enable function of a quad video op-amp (IC2) is used to multiplex and buffer the R/Chroma and Cvbs/Luma signal formats, and a dual video op-amp (IC1) buffers the BLUE and GREEN. This configuration is illustrated as an output SCART (Fig. 1), an Input SCART (Fig. 2), and a bi-directional SCART (Figure 3).

The dual and quad op amps are configured for non-inverting gains of two, using equal values of input and feedback resistance. The resistor values should not be large enough to create an in-band pole, or too small to be driven linearly. To achieve single-pin control for the Input or Output SCART, invert the Red/Cvbs enable and tie it to the Chroma/Luma enable. Separate resistors (Rdrive & Rterm) serve as drive and termination resistors.

Table 1: Pin assignments for the SCART connector

By enabling the Output SCART section with its inputs grounded, thereby connecting the RD/T resistors to ground through the op-amp outputs, the bi-directional SCART in Figure 3 uses the drive resistors (Rdrive) of the Output SCART section as termination resistors (RTerm) for the Input SCART section. For a typical Output SCART driven from a DAC, simply disabling the Output SCART will pull all the inputs to ground. Dedicated, multi-input SCART switches don't include the Y/Cvbs and C/Red multiplexing, but you can implement it externally using the quad op amp portion of the Input or Output SCART section.