Main D flip-flop chip model
74HC74 74LS90 Dual D Trigger 74LS74
74LS364 eight D flip-flop (three-state)
7474, 74 H74, 74F74, 74ALS74, 74L74, 74LS74A, 74S74, 74HC73, 74C74 Dual D-type positive-edge triggers (with preset and clear)
74174, 74LS174, 74F174, 74ALS174, 74S174, 74HC174, 74C174 Six D-type trigger (with clear end)
74175, 74LS175, 74F175, 74ALS175, 74S175, 74HC175, 74C175 Quad D-type trigger (with clear end)
74273, 74LS273, 74S273, 74F273, 74ALS273, 74HC273 Eight D-type trigger (with clear end)
74LS364 eight D flip-flop (three-state)
74LS377, 74F377, 74S3777 eight D trigger
74LS378, 74F378, 74S378, 74HC378 six D flip-flop
74LS379, 74F379, 74S379, 74HC379 eight D trigger
Advantages of EPON:
EPON adopts a point-to-multipoint structure and passive optical fiber transmission mode to provide multiple services on Ethernet. EPON technology integrates low-cost, high-bandwidth Ethernet equipment and low-cost optical fiber network technology. Compared with other access technologies, it has unique advantages, which are mainly reflected in the following aspects.
Good compatibility: EPON uses Ethernet technology, which is by far the most successful and mature LAN technology, and it can be said to be the mainstream of user LAN technology. Because EPON is only based on the existing IEEE 802.3 protocol, and realizes the transmission of Ethernet frames in the user access network through minor modifications and additions, EPON is basically compatible with Ethernet technology. Using Ethernet as the access network has low cost and good versatility, avoids complicated transmission protocols and format conversion, high efficiency, and simple management.
Low construction and maintenance costs: The EPON system significantly reduces the number of optical fibers, optical transceiver modules, and central office equipment. As the cost of optoelectronic devices continues to decrease, EPON`s per-line equipment access cost is comparable to ADSL and CM, especially the current price of optical fiber is lower than that of cable. These conditions have become the basis for the development of FTTH. At the same time, the foundation of EPON is Ethernet, and related components and equipment of Ethernet are the lowest in price. Using EPON as the access network has low cost and good versatility, eliminating the need for IP data transmission protocol and format conversion. High efficiency and simple management. In addition, there are only passive optical components such as optical fiber and optical splitter between the central office (OLT) and the user (ONU). There is no need to rent a computer room, no power supply, and no active equipment maintenance personnel. Therefore, it can effectively save operation and maintenance. cost.
High bandwidth: EPON can currently provide a downlink transmission rate of 1. 25 Gb/s, a single-wavelength uplink rate of 125 Mb/s, and can be upgraded to 1 GB/s with the development of Ethernet technology. This is much higher than the current access methods, which can meet the bandwidth requirements of various services such as broadband Internet access, video on demand, online games, video phones, and digital high-definition televisions, and fully meet the bandwidth requirements of access network customers. And it can easily and flexibly allocate bandwidth dynamically according to changes in user requirements, which can be used as the user's ultimate access method.
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