The MC44BS374CA is a multi-standard, PAL/NTSC modulator.
The channel is set by an on-chip high-speed I2C compatible bus receiver. A phase-locked loop (PLL) tunes the modulator over the full UHF range.
The modulator incorporates a sound subcarrier oscillator and uses a second PLL to derive 4.5, 5.5, 6.0, and 6.5 MHz subcarrier frequencies. These frequencies are selectable by bus.
The modulation standard can be chosen using a control bit that selects between positive and negative modulation.
The picture-to-sound ratio may be adjusted using the bus. In addition, an on-chip video test pattern generator can be switched ON with a 1 KHz audio test signal.