DS1996 Просмотр технического описания (PDF) - Maxim Integrated

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DS1996

64kbit Memory iButton

Maxim Integrated 

DS1996

Copy Scratchpad [55H]

This command is used to copy data from the scratchpad to memory. After issuing the copy scratchpad

command, the master must provide a 3-byte authorization pattern which is obtained by reading the

scratchpad for verification. This pattern must exactly match the data contained in the three address

registers (TA1, TA2, E/S, in that order). If the pattern matches, the AA (Authorization Accepted) flag

will be set and the copy will begin. A logic 0 will be transmitted after the data has been copied until a

reset pulse is issued by the master. Any attempt to reset the part will be ignored while the copy is in

progress. Copy typically takes 30 µs.

The data to be copied is determined by the three address registers. The scratchpad data from the

beginning offset through the ending offset, will be copied to memory, starting at the target address.

Anywhere from 1 to 32 bytes may be copied to memory with this command. Whole bytes are copied

even if only partially written. The AA flag will be cleared only by executing a write scratchpad

command.

Read Memory [F0H]

The read memory command may be used to read the entire memory. After issuing the command, the

master must provide the 2-byte target address. After the two bytes, the master reads data beginning from

the target address and may continue until the end of memory, at which point logic 1’s will be read. It is

important to realize that the target address registers will contain the address provided. The ending

offset/data status byte is unaffected.

The hardware of the DS1996 provides a means to accomplish error-free writing to the memory section.

To safeguard reading data in the 1-Wire environment and to simultaneously speed up data transfers, it is

recommended to packetize data into data packets of the size of one memory page each. Such a packet

would typically store a 16-bit CRC with each page of data to ensure rapid, error-free data transfers that

eliminate having to read a page multiple times to determine if the received data is correct or not. (See the

Book of DS19xx iButton Standards, Chapter 7 for the recommended file structure to be used with the 1-

Wire environment.)

1–WIRE BUS SYSTEM

The 1-Wire bus is a system which has a single bus master and one or more slaves. In all instances the

DS1996 is a slave device. The bus master is typically a microcontroller. The discussion of this bus

system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire

signaling (signal types and timing). A 1-Wire protocol defines bus transactions in terms of the bus state

during specified time slots that are initiated on the falling edge of sync pulses from the bus master. For a

more detailed protocol description, refer to Chapter 4 of the Book of DS19xx iButton Standards.

HARDWARE CONFIGURATION

The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to

drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open

drain connection or 3-state outputs. The 1-Wire port of the DS1996 is open drain with an internal circuit

equivalent to that shown in Figure 8. A multidrop bus consists of a 1-Wire bus with multiple slaves

attached. At regular speed the 1-Wire bus has a maximum data rate of 16.3k bits per second. The speed

can be boosted to 142k bits per second by activating the Overdrive Mode. The 1-Wire bus requires a

pullup resistor of approximately 5 kΩ.

The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus

MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low

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