| 摘要 |
PURPOSE: A cable modem for credit card checkers is provided to rapidly process the inquiry of credit cards by using a dedicated Internet network, especially a cable TV network, instead of a PSTN(Public Switched Telephone Network) or a PSDN(Public Switched Data Network). CONSTITUTION: A cable modem(300) is comprised of a tuner(310), a modulator(320), a demodulator(330), an MAC(Media Access Control) processor(340), a microprocessor(350), a flash memory(360), a RAM(370), and a serial communication interface(380). The tuner(310) selects the signal components of about 6-40MHz among the signals of about 88-860MHz of a downstream packet inputted through an F-connector from a CMTS(Cable Modem Termination System). The modulator(320) modulates an upstream packet, transferred from the MAC processor(340), through hexadecimal QAM(Quadrature Amplitude Modulation) or QPSK(Quadrature Phase Shift Keying), creates an upstream packet modulation signal, and transmits it to the CMTS through the tuner(310) and the F-connector. The demodulator(330) receives and demodulates the IF(Intermediate Frequency) signals of 6-40MHz, selected by the tuner(310) and transfers the demodulated downstream packet to the MAC processor(340). The MAC processor(340) reads upstream data from the RAM(370) through DMA(Direct Memory Access), creates an upstream packet according to an appointed MAC frame format, and transfers it to the modulator(330).
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