DS2432X 데이터 시트보기 (PDF) - Maxim Integrated

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DS2432X

1Kb Protected 1-Wire EEPROM with SHA-1 Engine

Maxim Integrated 

ABRIDGED DATA SHEET

DS2432

ROM FUNCTION COMMANDS

Once the bus master has detected a presence, it can issue one of the seven ROM function commands that

the DS2432 supports. All ROM function commands are eight bits long. A list of these commands follows

(refer to flowchart in Figure 9):

Read ROM [33h]

This command allows the bus master to read the DS2432’s 8-bit family code, unique 48-bit serial

number, and 8-bit CRC. This command should only be used if there is a single slave 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 resultant family code and 48-bit serial number

read by the master will be invalid.

Match ROM [55h]

The match ROM command, followed by a 64-bit registration number, allows the bus master to address a

specific DS2432 on a multidrop bus. Only the DS2432 that exactly matches the 64-bit registration

number will respond to the following memory function command. All other slaves will wait for a reset

pulse. This command can be used with a single or multiple devices on the bus.

Search ROM [F0h]

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 registration numbers. The search ROM command allows the bus master to use

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

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

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

number. After one complete pass, the bus master knows the 64-bit number of one device. Additional

passes will identify the registration numbers of the remaining devices. Refer to Application Note 187 for

a detailed discussion of a search ROM, including an actual example.

Skip ROM [CCh]

This command can save time in a single drop bus system by allowing the bus master to access the

memory and SHA-1 functions without providing the 64-bit registration number. If more than one slave is

present on the bus and, for example, a read command is issued following the Skip ROM command, data

collision will occur on the bus as multiple slaves transmit simultaneously (open-drain pulldowns will

produce a wired-AND result).

Overdrive Skip ROM [3Ch]

On a single-drop bus this command can save time by allowing the bus master to access the memory and

SHA-1 functions without providing the 64-bit registration number. Unlike the normal Skip ROM

command the Overdrive Skip ROM sets the DS2432 in the Overdrive Mode (OD = 1). All

communication following this command code has to occur at Overdrive Speed until a reset pulse of

minimum 480 µs duration resets all devices on the bus to regular speed (OD = 0).

When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive

mode. To subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed

has to be issued followed by a Match ROM or Search ROM command sequence. This will speed up the

search process. If more than one Overdrive-supporting slave is present on the bus and the Overdrive Skip

ROM command is followed by a read command, data collision will occur on the bus as multiple slaves

transmit simultaneously (open drain pulldowns will produce a wired-AND result).

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