DM336P Davicom Semiconductor Incorporated, DM336P Datasheet - Page 17
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DM336P
Manufacturer Part Number
DM336P
Description
Manufacturer
Davicom Semiconductor Incorporated
Datasheet
1.DM336P.pdf
(40 pages)
(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,
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
Final
Version: DM336P-DS-F02
August 15, 2000
hardware drives the entire 8-bit data bus, but
checks only the lower 2 bits.
Checksum
BYTE
7:0
BYTE BYTE BYTE BYTE BYTE BYTE
7:0
Serial Number
7:0
V.34 Integrated Data/ Fax/Voice/Speakerphone Modem Device Set
Table 2. Shifting of Serial Identifier
7:0
7:0
7:0
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.
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.
7:0
Vendor ID
BYTE
7:0
BYTE
7:0
SHIFT
DM336P
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