baud rate generator - with six switchable settings

A with six switchable settings Most asynchronous receiver/transmit- ters (generally known as UARTs) operate at a clock frequency which is sixteen times the transmission rate. There are special ICs available that are dedicated to this particular timing function but they are neither freely available nor cheap. The classic switchable oscillator/divider circuit is, however, a good substitute. The clock frequencies provided in the design shown here correspond to the standard transmission rates of 1200, 600, 300, 150, 110 and 75 baud. The oscillator is based on inverters N1 and N2, in combination with the 1 MHz crystal. Its signal is fed, via N3, to the first 4024. A flip-flop, con- sisting of N9 and N10, is included in the reset line to this divider to ensure that the reset is perfectly synchron- ised with the clock signal. The out- put signal from IC1 feeds the clock input of the second 4024, which can be "programmed" by means of S1 (a double-pole six-way wafer switch). The reset puls...