DS2401 参数 Datasheet PDF下载

DS2401

TRANSACTION SEQUENCE

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Initialization

ROM Function Command

Read Data

The sequence for accessing the DS2401 via the 1-Wire port is as follows:

All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence

consists of a reset pulse transmitted by the bus master followed by a Presence Pulse(s) transmitted by the

slave(s).

The Presence Pulse lets the bus master know that the DS2401 is on the bus and is ready to operate. For

more details, see the 1-Wire Signaling section.

INITIALIZATION

ROM FUNCTION COMMANDS

Once the bus master has detected a presence, it can issue one of the four ROM function commands. All

ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure

4).

Read ROM [33h] or [0Fh]

This command allows the bus master to read the DS2401’s 8-bit family code, unique 48-bit serial

number, and 8-bit CRC. This command can only be used if there is a single DS2401 on the bus. If more

than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same

time (open drain will produce a wired-AND result). The DS2401 Read ROM function will occur with a

command byte of either 33h or 0Fh in order to ensure compatibility with the DS2400, which will only

respond to a 0Fh command word with its 64-bit ROM data.

The complete 1-Wire protocol for all Maxim iButtons® contains a Match ROM and a Skip ROM

command. Since the DS2401 contains only the 64-bit ROM with no additional data fields, the Match

ROM and Skip ROM are not applicable and will cause no further activity on the 1-Wire bus if executed.

The DS2401 does not interfere with other 1-Wire parts on a multidrop bus that do respond to a Match

ROM or Skip ROM (for example, a DS2401 and DS1994 on the same bus).

When a system is initially brought up, the bus master might not know the number of devices on the 1-

Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process

of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process

is the repetition of a simple 3-step routine: read a b it, read the complement of the bit, then write the

desired value of that bit. The bus master performs this simple 3-step routine on each bit of the ROM.

After one complete pass, the bus master knows the contents of the ROM in one device. The remaining

number of devices and their ROM codes may be identified by additional passes. Refer to

Application

Note 187: 1-Wire Search Algorithm

for a comprehensive discussion of a ROM search, including an actual

example.

iButton is a registered trademark of Maxim Integrated Products, Inc.

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Match ROM [55h] / Skip ROM [CCh]

Search ROM [F0h]