DS2450

4 of 24

102199

64-BIT LASERED ROM Figure 3

1-WIRE CRC-GENERATOR Figure 4

DEVICE REGISTERS

All registers of the DS2450 are mapped into a linear memory range of 24 adjacent bytes organized as

three 8-byte pages. The first page, called conversion read-out, contains the memory area where the chip-

internal logic places the results of a conversion for the bus master to read. Starting with channel A at the

lowest address, each channel has an area of 16 bits assigned for the conversion result, as shown in Figure

5a. The power-on default for the conversion read-out registers is all zeros. Regardless of the resolution

requested, the most significant bit of the conversion is always at the same bit position. If less than 16-bit

resolution is requested, the least significant bits of the conversion result will be filled with zeros in order

to always generate a 16-bit result. For applications that require less than four analog inputs, one should

start using input D for the first channel, input C for the second one, etc. The advantage is that when

reading the conversion results one reaches the end of the page and with it the CRC16 sooner and

minimizes the traffic on the 1-Wire bus. For more details on reading please refer to the Read Memory

command description.

MEMORY MAP PAGE 0, CONVERSION READ-OUT Figure 5a

Address

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

00

A

A

A

A

A

A

A

LSBIT A

01

MSBIT A

A

A

A

A

A

A

A

02

B

B

B

B

B

B

B

LSBIT B

03

MSBIT B

B

B

B

B

B

B

B

04

C

C

C

C

C

C

C

LSBIT C

05

MSBIT C

C

C

C

C

C

C

C

06

D

D

D

D

D

D

D

LSBIT D

07

MSBIT D

D

D

D

D

D

D

D

The control and status information for all channels is located in memory page 1 (Figure 5b). As for the

conversion read-out, each channel has assigned 16 bits. The four least significant bits, called RC3 to

RC0, are an unsigned binary number that represents the number of bits to be converted. A code of 1111

(15 decimal) will generate a 15-bit result. For a full 16-bit conversion the code number needs to be 0000.

The next two bits beyond RC3 will always read 0. They have no function and cannot be changed to 1s.