DS2480 datasheet(6/26 Pages) DALLAS

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DS2480

042498 6/26

COMMUNICATION COMMAND CODES Table 1

FUNCTION

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3, BIT 2

BIT 1

BIT 0

Single Bit

0 = write 0

1 = write 1

reg. speed

flex. speed

OD. speed

reg. speed

See Text

Accelerator

Control

0 = accelerator off

1 = accelerator on

See Text

reg. speed

flex. speed

OD. speed

reg. speed

Reset

(don’t care)

reg. speed

flex. speed

OD. speed

reg. speed

Pulse

0 = 5V strong pull–up

1 = 12V prog. pulse

pulse

See Text

COMMUNICATION COMMAND RESPONSE Table 2

FUNCTION

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

Single Bit

same as sent

1–Wire read back,

both bits same value

Reset

See

Text

00 = 1–Wire shorted

01 = presence pulse

10 = alarming presence

pulse

11 = no presence pulse

Pulse

same as sent

undefined

(The Search Accelerator Control command does not generate a response byte.)

Reset

The Reset command must be used to begin all 1–Wire

communication. The speed selection included in the

command code immediately takes effect. The response

byte includes a code for the reaction on the 1–Wire bus

(bits 0 and 1) and a code for the chip revision (bits 2 to 4).

If bit 5 of the response byte reads ‘1’, a programming

voltage is present on the VPP pin, indicating that one

may try programming EPROM devices.

Single Bit

The Single Bit command is used to generate a single

time slot on the 1–Wire bus at the speed indicated by

bits 2 and 3. The type of the time slot (write zero or write

one) is determined by the logic value of bit 4. A read data

time slot is identical to the write one time slot. Bits 0 and

1 of the response byte transmitted by the DS2480 at the

end of the time slot reveal the value found on the 1–Wire

bus when reading.

For a time slot without a subsequent strong pull–up, bit 1

of the command must be set to 0. For a time slot immedi-

ately followed by a strong pull–up bit 1 must be set to 1.

As soon as the strong pull–up is over, the device will

send a second response byte, code EFh (read 1) or ECh

(read 0), depending on the value found on the 1–Wire

bus when reading. The strong pull–up directly following

the single bit is used in conjunction with the Crypto

iButton.

Search Accelerator Control

The Search Accelerator Control command is used to set

or reset the Search Accelerator control flag. Bit 4 of the

command code contains the state to which the acceler-

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