DM560P データシートの表示（PDF） - Davicom Semiconductor, Inc.

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DM560P

V.90 Integrated Data/Fax/Voice/Speakerphone Modem Device Set

Davicom Semiconductor, Inc. 

DM560P

V.90 Integrated Data/Fax/Voice/Speakerphone Modem Device Set

Hardware Protocol

The isolation protocol can be invoked by the Plug

and Play software at any time. The Initiation Key will

put 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 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.

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."

After 64 bits have been read, the 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.

There are two other special considerations for

software protocol. During an iteration, it is possible

that the 55H and AAH combination is never

detected. It is also possible that the checksum does

not match. If either of these cases occurs on the first

iteration, it must be assumed that the READ_DATA

port is in conflict. If a conflict is detected, then the

READ_DATA port will be relocated. The above

process is repeated until a non-conflicting location

for the READ_DATA port is found. The entire range

between 203H and 3FFH is available; however, in

practice, it is expected that only a few locations will

be tried before software determines that no Plug and

Play cards are present.

During subsequent iterations, the occurrence of

either of these two special cases should be

interpreted as the absence of any further Plug and

Play cards (i.e. the last card was found in the

previous iteration). This terminates the isolation

protocol.

Note: The software must delay 1 msec prior to

starting the first pair of isolation reads, and wait 250

msec between each sub-sequence pair of isolation

reads. This delay gives the ISA card time to access

information from slow storage devices.

20

Preliminary

Version: DM560P-DS-P07

August 11, 2000

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