modem essays

modem essays Implementing a Single-Chip Once I was given the task to implement a modem chip, I immediately started to search for the various available types of such chips. The resulting searches gave me a large range of modem chips. The divide between most of the I.C.s found was whether the modem was so-called single-chip or dual-chip. The latter involves the same circuitry as in the single-chip modem but has another chip dedicated to DSP (digital signal processing) and some memory (both RAM and ROM). These chips were found to be too complex and beyond the scope of our requirements. On the other hand the single-chip modems found were also divided into two main types, being those with or without a microcontroller. The latter are not numerous and were initially thought to not even be viable, but upon further detailed research such I.C.s were actually found. The modem chip selected for this purpose is the MSM6926 produced by OKI. The following is a detailed description of the chip and its various functions: The MSM6926 is OKI's 300 bps single chip modem series which transmit and receive serial, binary data over a switched telephone network using frequency shift keying (FSK). FSK is one of the modulation schemes available for data transmission, and is one the most common. Other modulation schemes include ASK, BPSK and QAM but FSK was found sufficient in our case. The MSM6926 is compatible with ITU-T V.21 series data sets, where the ITU-T V.21 is data transfer protocol dictating the different frequencies for the FSK transmission. This device provides all the necessary modulation, demodulation, and filtering required to implement a serial, asynchronous communication link. OKI's single chip modem series is designed for users who are not telecommunication experts and are easy to use cost effective alternative to standard discrete modem design. CMOS LSI technology provides the ...