DS1925 datasheet(28/46 Pages) MAXIM

28 / 46 page

The DS1925 uses a control function command to stop

a mission. Only a mission that is in progress can be

stopped. After the strong pullup, an FFh dummy byte is

then read followed by a repeating result byte. If pass-

words are enabled and the transmitted password is differ-

ent from the stored full-access password, the XPC Stop

Mission command fails. If the password was correct or if

passwords were not enabled, the device clears the MIP bit

in the General Status register and restores write access

to the register pages. The Mission Backup Registers are

written on a XPC Stop Mission command. See Figure 15.

XPC Read Memory [44h]

The XPC Read Memory command is a subcommand of

the external power command. The command is applicable

to the entire user memory and the datalog memory. The

command can be used at any time, regardless of the bat-

tery status.

The bus master sends the XPC command code [66h],

length byte [0Bh], XPC Read Memory command code

[44h], TA1 address byte, and TA2 address byte. Next,

the master must transmit one of the 64-bit passwords fol-

lowed by release bytes [FFh], and strong pullup and delay

of tSTD. If passwords are enabled and the transmitted

password does not match one of the stored passwords,

the XPC Read Memory command fails. The device reads

the invalid password repeat byte instead of data memory.

If the password was correct or if passwords were not

enabled, the master reads data from the DS1925 begin-

ning from the starting address and continuing until the end

of the block is reached. Block size is determined by the

upper bits of TA2 as described below. At that point, the

bus master sends 16 additional read data time slots and

receives the inverted 16-bit CRC. Immediately following

the CRC, the master can issue another release byte, and

strong pullup and delay of tSTD to read the next block.

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 DS1925 transmits

00h or FFh bytes. The CRC at the end of a block is based

on the data as it was transmitted.

With the initial pass through the XPC Read Memory flow,

the 16-bit CRC value is the result of shifting the XPC

command byte, length byte, XPC Read Memory sub-com-

mand, followed by the two address bytes and the 8 bytes

of password. Subsequent passes through the flow gener-

ate a 16-bit CRC that is the result of clearing the CRC

generator and then shifting in the contents of the data

memory page. After the 16-bit CRC of the last block is

read, the bus master receives logical 1s from the DS1925

until a reset pulse is issued. The XPC Read Memory com-

mand sequence can be ended at any point by issuing a

reset pulse outside of the reserved strong pullup times.

To access the entire memory space, the two most sig-

nificant bits of TA2 can be used to change the address

encoding. Reference Figure 8 for target address bit map.

If T15 = 0, address (T14-T0) is used as a starting byte

address which is limited to 215. The following mode is

used to start at higher pages. If T15 = 1, address (T13-T0)

is used as a starting page number. In addition if the user

is reading the data-log memory, T14 = 1 increases the

block size to 64 bytes, or 2 pages. The T14 = 1 large block

mode is only available for the datalog memory space.

The Mission Backup Register backup copies are written

when the last mission was started. Not all of the fields are

backed up. The only fields that are valid in this condition

are: sample rate (0206h to 0207h), temperature alarm

(0208h to 0209h), temperature alarm enable (0210h), RTC

enable (0212h), miscellaneous control (0213h), start delay

counter (0216h to 0218h), mission time stamp (0219h to

021Ch), mission sample counter (0220h to 0222h), and

device samples counter (0223h to 0225h). To compute the

new mission sample counter and device sample counter

at the time the battery depleted, the log must be read. The

end of long can be determined when the readings are FFh.

See Figure 15.

XPC Clear Memory [96h]

The XPC Clear Memory command is used to prepare the

device for another mission by clearing the log or to clear the

user memory. This command is only executed to clear the

log memory if no mission is in progress. XPC clear memory

is a subcommand to the general-purpose XPC command

66h. The XPC command (66h) is sent first, followed by a

length byte (0Ah), the subcommand (96h), the parameter

byte 00h for user memory or 01h for log memory, and then

the password. After that the device responds with a CRC-

16 of the preceding bytes. After this sequence the master

sends an FFh release byte followed by a strong pullup and

delay (tLSTD for user memory and tCML for log memory).

If passwords are enabled and the transmitted password

is different from the stored full-access password or a mis-

sion is in progress, the XPC Clear Memory command fails.

The success or failure of the command is indicated by the

repeat byte that is read after the strong pullup delay. If the

password was correct or if passwords were not enabled

DS1925

iButton High-Capacity Temperature Logger

with 122KB Data-Log Memory

www.maximintegrated.com

Maxim Integrated │ 28

DS1925 датащи(PDF) 28 Page - Maxim Integrated Products

DS1925 датащи(HTML) 28 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

датащи скачать

ссылки URL