DS2422 Maxim, DS2422 Datasheet - Page 22

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

SERIAL DATA INTERFACE TUNING
The serial interface consists of several signals that are intended to control external circuitry, such as an analog-to-
digital converter (see Figure 9A). There is one signal, called CNVST, which can be used to load data into a shift
register or to trigger a data conversion. The delay t
CNVST is user-programmable through the Delay Register. When used with a charge pump such as the MAX619,
the variable delay t
charge pump is used, the delay may be set to 00h to begin the conversion sooner.
Delay Register
During a mission, there is only read access to this register.
The Delay Register holds the preset value of a counter that determines the duration of t
unsigned integer with values ranging from 0 to FFh (0 to 255 decimal). This is equivalent to a range from 0 to
127.5ms. The power-on value of this register is 08h.
TEMPERATURE CONVERTER TRIM
The DS2422 leaves the factory fully tested, but not trimmed for temperature accuracy. The actual trim values
consist of two sets, Temperature Counter Reset and Temperature Conversion Length, which need to be
determined individually for each device during a 2-point calibration step. These trim values need to be written to the
respective registers in the Trim Register Page before the device meets the accuracy specification shown in the
graphs at the beginning of this document.
Temperature Counter Reset Register
There is always full read/write access to this register. Bits 5-7 of the High Byte are always 0 and cannot be written
to 1. The power-on default is 6Bh (0404h) and 11h (0405h).
The Temperature Counter Reset value provides a purely vertical shift along the Temperature Transfer Curve in
order to reset the zero point. The algorithm to determine the correct Temperature Counter Reset value is included
in Application Note 2810.
Temperature Conversion Length Register
There is always full read/write access to this register. Bits 5-7 of the High Byte are always 0 and cannot be written
to 1. The power-on default is A6h (0406h) and 12h (0407h).
The Temperature Conversion Length value provides a vertical and horizontal shift of the Temperature Transfer
Curve. The algorithm to determine the correct Temperature Counter Reset value is included in Application Note
2810.
DATALOG MEMORY USAGE
Once setup for a mission, the DS2422 logs the temperature measurements and/or external data at equidistant time
points entry after entry in its datalog memory. The datalog memory is able to store 8192 entries in 8-bit format or
4096 entries in 16-bit format (Figure 10A). If temperature as well as external data is logged, both in the same
format, the memory is split into two equal sections that can store 4096 8-bit entries or 2048 16-bit entries (Figure
10B). If the device is set up to log data in different formats, e. g., temperature in 8-bit and external data in 16-bit
format, the memory is split into blocks of different size, accommodating 2560 entries for either data source (Figure
10C). In this case, the upper 256 bytes are not used. In 16-bit format, the higher 8 bits of an entry are stored at the
ADDR
0400h
ADDR
0404h
0405h
ADDR
0406h
0407h
b7
b7
b7
0
0
SP
is used to give the charge pump adequate time to stabilize before a conversion starts. If no
b6
b6
b6
0
0
Temperature Conversion Length Low Byte
Temperature Counter Reset Low Byte
b5
b5
b5
0
0
Temp Conversion Length High Byte
b4
b4
b4
delay value
Temperature Counter Reset High Byte
SP
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b3
b3
b3
from the activation of the serial interface (PUMP_ONZ) to
b2
b2
b2
b1
b1
b1
b0
b0
b0
SP
. The number format is