Rainbow-electronics DS1920 Bedienungsanleitung PDF herunterladen (Seite 8)

DS1920

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1-WIRE CRC CODE Figure 6

MEMORY

The DS1920’s memory is organized as shown in Figure 7. The memory consists of a scratchpad and 2

bytes of EEPROM which store the high and low temperature triggers TH and TL. The scratchpad helps

insure data integrity when communicating over the 1-Wire bus. Data is first written to the scratchpad

where it can be read back. After the data has been verified, a copy scratchpad command will transfer the

data to the EEPROM. This process insures data integrity when modifying the memory.

The scratchpad is organized as 8 bytes of memory. The first 2 bytes contain the measured temperature

information. The 3

and 4

bytes are volatile copies of TH and TL and are refreshed with every power-on

reset. The next 2 bytes are not used; upon reading back, however, they will appear as all logic 1s. The 7

and 8

bytes are count registers, which may be used in obtaining higher temperature resolution (see

“Operation-Measuring Temperature” section).

There is a 9

byte which may be read with a Read Scratchpad command. This byte is a cyclic redundancy

check (CRC) over all of the 8 previous bytes. This CRC is implemented as described in the section titled

“CRC Generation.”

DS1920 MEMORY MAP Figure 7

SCRATCHPAD BYTE EEPROM

TEMPERATURE LSB 0

TEMPERATURE MSB 1

TH/USER BYTE 1 2 TH/USER BYTE 1

TL/USER BYTE 2 3 TL/USER BYTE 2

RESERVED 4

RESERVED 5

COUNT REMAIN 6

COUNT PER °C 7

CRC 8

1-WIRE BUS SYSTEM

The 1-Wire bus is a system which has a single bus master and one or more slaves. The DS1920 behaves

as a slave. The discussion of this bus system is broken down into three topics: hardware configuration,

transaction sequence, and 1-Wire signaling (signal types and timing).

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Rainbow-electronics DS1920 Bedienungsanleitung Seite 8