DS1925 datasheet(27/46 Pages) MAXIM

27 / 46 page

External Power Command (XPC) [66h]

The external power command is a gateway command that

allows subcommands to operate using an external strong

pullup. The XPC command is followed by a length byte,

the sub-command, and its parameter bytes. The master

then receives a CRC16, transmits an FFh dummy byte,

and enables the strong pullup.

XPC Copy Scratchpad [99h]

The XPC Copy Scratchpad command is a subcommand of

the external power command. This command is used to copy

data from the scratchpad to the writable memory sections.

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

length byte [0Ch], XPC Copy Scratchpad command code

[99h], TA1 address byte, TA2 address byte, and E/S byte.

These three bytes are the authorization sequence and

can be verified using a Read Scratchpad command. Next,

the master must transmit the full-access 64-bit password.

At this point, the bus master sends 16 additional read

data time slots and receives the inverted 16-bit CRC. If

the CRC is correct, the master then sends the release

byte [FFh], and strong pullup and delay of tLSTD or tLSTD

+ tSRTC. The additional tSRTC delay is required if this

RTC is being enabled with this command and the device

is in the Clear Memory state or in an unknown state. If

passwords are enabled and the transmitted password

is different from the stored full-access password, the XP

Copy Scratchpad command fails. 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 (authorization accepted) flag is

set and the copy begins. After the required strong pullup

delay, an FFh dummy byte is then read followed by a

repeating result byte. The repeating byte is transmitted

until the master issues a reset pulse to indicate success

or an error condition.

The data to be copied is determined by the three address

registers. The scratchpad data from the beginning offset

through the ending offset is copied, starting at the target

address. The AA flag remains at logic 1 until it is cleared

by the next Write Scratchpad command. With a suitable

password, the XPC Copy Scratchpad always functions

for the 16 pages of data memory. While a mission is in

progress, write attempts to the register pages are not suc-

cessful. The AA bit remaining at 0 indicates this.

XPC Start Mission [DDh]

The XPC Start Mission command is a subcommand of the

external power command. This command is used to start

a temperature logging mission

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

length byte [09h], XPC Start Mission command code [DDh],

64-bit full-access password. At this point, the bus master

sends 16 additional read data time slots and receives the

inverted 16-bit CRC. If the CRC is correct, the master then

sends the release byte [FFh], and strong pullup and delay

of tLSTD or tLSTD + tSRTC. The additional tSRTC delay

is required if this RTC was not already enabled and the

device is in the Clear Memory State or in an unknown state.

A new mission can only be started if the previous mis-

sion has been ended and the memory has been cleared.

After the strong pullup, an FFh dummy byte is then read

followed by a repeating result byte. A repeating result

byte of 77h Invalid Parameter indicates that the selected

sample rate is less than 3 minutes and is not supported.

If passwords are enabled and the transmitted password

is different from the stored full-access password, the XP

Start Mission command fails with a repeating result byte

of 11h Invalid Password. If the password was correct or if

passwords were not enabled, the device starts a mission.

If SUTA = 0, the sampling begins as soon as the mission

start delay is over. If SUTA = 1, the first sample is written

to the data-log memory at the time the temperature alarm

occurred. At this point the Mission Sample Counter incre-

ments and the Mission Timestamp is set and the regular

sampling and logging begins. While the device is waiting

for a temperature alarm to occur, the WFTA flag in the

General Status register reads 1. During a mission there

is only read access to the register pages. The Mission

Backup Registers are written on a XPC Start Mission

command. See Figure 15.

XPC Stop Mission [BBh]

The XPC Stop Mission command is a subcommand of the

external power command. This command is used to stop

a temperature logging mission

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

length byte [09h], XPC Stop Mission command code

[BBh], 64-bit full-access password. At this point, the bus

master sends 16 additional read data time slots and

receives the inverted 16-bit CRC. If the CRC is correct,

the master then sends the release byte [FFh], and strong

pullup and delay of tLSTD.

DS1925

iButton High-Capacity Temperature Logger

with 122KB Data-Log Memory

www.maximintegrated.com

Maxim Integrated │ 27

DS1925 датащи(PDF) 27 Page - Maxim Integrated Products

DS1925 датащи(HTML) 27 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