| 摘要 |
<p>An all digital modem includes a clock divider (49, 63) for generating four waveforms (65, 67, 69, 71) at a desired transmission frequency but mutually phase shifted by 90 degrees, a first microprocessor (31) programmed to receive digital data (33) at its input, to convert the data into dibits and to select as a modem output (81) one of the four waveforms phase shifted 90 degrees with respect to each other. To demodulate incoming signals, a zero crossing detector (107) detects zero crossings of an incoming modulated signal, a second microprocessor (127) coupled to the zero crossing detector (107) receives the zero crossing information along with parity information and converts the information into dibits, and a third microprocessor (128) receives dibit outputs from the second microprocessor (127) and converts the dibits into a serial stream of data (133) at essentially constant frequency.</p> |
