DS9101 datasheet(30/55 Pages) MAXIM

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Read Scratchpad [AAh]

This command is used to verify scratchpad data and

target address. After issuing the Read Scratchpad

command, the master begins reading. The first 2 bytes

are the target address. The next byte is the ending off-

set/data status byte (E/S) followed by the scratchpad

data beginning at the byte offset T[4:0], as shown in

Figure 8. The master can continue reading data until

the end of the scratchpad after which it receives an

inverted CRC-16 of the command code, target

addresses TA1 and TA2, the E/S byte, and the scratch-

pad data starting at the target address. After the CRC

is read, the bus master reads logic 1s from the DS1923

until a reset pulse is issued.

Copy Scratchpad [with Password] [99h]

This command is used to copy data from the scratch-

pad to the writable memory sections. After issuing the

Copy Scratchpad command, the master must provide a

3-byte authorization pattern, which can be 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). Next,

the master must transmit the 64-bit full access pass-

word. If passwords are enabled and the transmitted

password is different from the stored full access pass-

word, the Copy Scratchpad command fails. The device

stops communicating and waits for a reset pulse. If the

password was correct or if passwords were not

enabled, the device tests the 3-byte authorization code.

If the authorization code pattern matches, the AA flag is

set and the copy begins. A pattern of alternating 1s and

0s is transmitted after the data has been copied until

the master issues a reset pulse. While the copy is in

progress, any attempt to reset the part is ignored. Copy

typically takes 2μs per byte.

The data to be copied is determined by the three

address registers. The scratchpad data from the begin-

ning offset through the ending offset are copied, start-

ing at the target address. The AA flag remains at logic

1 until it is cleared by the next Write Scratchpad com-

mand. With suitable password, the copy scratchpad

always functions for the 16 pages of data memory and

the 2 pages of calibration memory. While a mission is in

progress, write attempts to the register pages are not

successful. The AA bit remaining at 0 indicates this.

Read Memory with [Password

and] CRC [69h]

The Read Memory with CRC command is the general

function to read from the device. This command gener-

ates and transmits a 16-bit CRC following the last data

byte of a memory page.

After having sent the command code of the Read

Memory with CRC command, the bus master sends a

2-byte address that indicates a starting byte location.

Next, the master must transmit one of the 64-bit pass-

words. If passwords are enabled and the transmitted

password does not match one of the stored passwords,

the Read Memory with CRC command fails. The device

stops communicating and waits for a reset pulse. If the

password was correct or if passwords were not

enabled, the master reads data from the DS1923

beginning from the starting address and continuing

until the end of a 32-byte page is reached. At that point

the bus master sends 16 additional read-data time slots

and receives the inverted 16-bit CRC. With subsequent

read-data time slots the master receives data starting at

the beginning of the next memory page followed again

by the CRC for that page. This sequence continues

until the bus master resets the device. When trying to

read the passwords or memory areas that are marked

as “reserved,” the DS1923 transmits 00h or FFh bytes,

respectively. The CRC at the end of a 32-byte memory

page is based on the data as it was transmitted.

With the initial pass through the Read Memory with

CRC flow, the 16-bit CRC value is the result of shifting

the command byte into the cleared CRC generator fol-

lowed by the 2 address bytes and the contents of the

data memory. Subsequent passes through the Read

Memory with CRC flow generate a 16-bit CRC that is

the result of clearing the CRC generator and then shift-

ing in the contents of the data memory page. After the

16-bit CRC of the last page is read, the bus master

receives logic 1s from the DS1923 until a reset pulse is

issued. The Read Memory with CRC command

sequence can be ended at any point by issuing a reset

pulse.

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

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