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DM336P 数据表(PDF) 17 Page - List of Unclassifed Manufacturers |
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DM336P 数据表(HTML) 17 Page - List of Unclassifed Manufacturers |
17 / 40 page DM336P V.34 Integrated Data/ Fax/Voice/Speakerphone Modem Device Set Final 17 Version: DM336P-DS-F02 August 15, 2000 (5) Serial Identifier The key element of the Plug and Play isolation protocol is that each card contains a unique number called a serial identifier. The serial identifier is a 72-bit unique, non-zero number composed of two 32 bit fields and 8-bit checksum. The first 32-bit field is a vendor identifier. The other 32-bits can be any value, such as a serial number, part of a LAN address, or a static number, as long as no two cards in a single system will ever have the same 64-bit number. The serial identifier is accessed bit-serially by isolation logic, and is used to differentiate the cards. Checksum Serial Number Vendor ID BYTE BYTE BYTE BYTE BYTE BYTE BYTE BYTE BYTE 7:0 7:0 7:0 7:0 7:0 7:0 7:0 7:0 7:0 SHIFT Table 2. Shifting of Serial Identifier The shift order for all Plug and Play serial isolation and resource data is defined as bit [0], bit [1], and so on through bit [7]. (6) Hardware Protocol The isolation protocol can be invoked by the Plug and Play software at any time. The previously described Initiation Key puts all cards into configuration mode. The hardware on each card expects 72 pairs of I/O read accesses to the READ_DATA port. The card ’s response to these reads depends on the value of each bit of the serial identifier, which is examined one bit at a time, as shown in Table 2. If the current bit of the serial identifier is a "1," then the card will drive the data bus to 55H to complete the first I/O read cycle. If the bit is a “0,” then the card puts its data bus driver into high impedance. All cards in high impedance will check the data bus during the I/O read cycle to sense if another card is driving SD[1:0] to "01." During the second I/O read, the card(s) that drove the 55H will now drive a AAH. All high impedance cards will check the data bus to sense if another card is driving SD [1:0] to "10." If a high impedance card senses another card driving the data bus with the appropriate data during both cycles, it ceases to participate in the current iteration of card isolation. Such cards, which lose out, will participate in future iterations of the isolation protocol. Note: During each read cycle, the Plug and Play hardware drives the entire 8-bit data bus, but checks only the lower 2 bits. If a card is driving the bus or is in high impedance state and does not sense another card driving the bus, then it should prepare for the next pair of I/O reads. The card shifts the serial identifier by one bit, using the shifted bit to decide its response. The above sequence is repeated for the entire 72-bit serial identifier. At the end of this process, one card remains. This card is assigned a handle referred to as the Card Select Number (CSN) that will be used later to select the card. Cards that have been assigned a CSN will not participate in subsequent iterations of the isolation protocol. Cards must be assigned a CSN before they will respond to the other PnP commands. (7) Software Protocol The Plug and Play software sends the Initiation Key to all Plug and Play cards to place them into configuration mode. The software is then ready to perform the isolation protocol. The Plug and Play software generates 72 pairs of I/O read cycles from the READ_DATA port. The software checks the data returned from each pair of I/O reads for the 55H or AAH driven by the hardware. If both 55H or AAH are read back, then the software assumes that the hardware has a "1" bit in that position. All other bits are assumed to be a "0." During the first 64 bits, software generates a checksum using the received data. The checksum is compared with the checksum read back in the last 8 bits of the sequence. |
类似零件编号 - DM336P |
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类似说明 - DM336P |
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