DM336P Просмотр технического описания (PDF) - Unspecified

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DM336P

V.34 Integrated Data/ Fax/Voice/Speakerphone Modem Device Set

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DM336P

V.34 Integrated Data/ Fax/Voice/Speakerphone Modem Device Set

(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.

Final

17

Version: DM336P-DS-F02

August 15, 2000

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