Rainbow-electronics DS1821 Uživatelský manuál stáhnout pdf (Strana 10)

DS1821

Page 10 of 17

DS1821 FUNCTION COMMAND SET Table 4

Command Description Protocol

1-Wire Bus Activity

After Command is Issued

TEMPERATURE CONVERSION COMMANDS

Read

Temperature

Reads last converted temperature

value from temperature register.

AAh Master receives 8-bit temperature

value from DS1821.

Start Convert T Initiates temperature conversions. EEh None

Stop Convert T Halts temperature conversions. 22h None

THERMOSTAT and STATUS/CONFIGURATION COMMANDS

Write TH Writes data to the T

value to

DS1821.

Write TL Writes data to the T

value to

DS1821.

Read TH Reads data from the T

value from

DS1821.

Read TL Reads data from the T

value from

DS1821.

Write Status Writes data to the

status/configuration register.

0Ch Master transmits 8-bit

status/configuration value to DS1821.

Read Status

Reads data from the

status/configuration register.

ACh

Master receives 8-bit

status/configuration value from

DS1821.

HIGH-RESOLUTION COMMANDS

Read Counter

Reads data from the counter

A0h

Master receives 9-bit counter value

from DS1821.

Load Counter Loads slope accumulator data into

the counter register

41h None

1-WIRE SIGNALING

The DS1821 uses a strict 1-wire communication protocol to insure data integrity. Several signal types are

defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these

signals, with the exception of the presence pulse, are initiated by the bus master.

INITIALIZATION PROCEDURE: RESET AND PRESENCE PULSES

All communication with the DS1821 begins with an initialization sequence that consists of a reset pulse

from the master followed by a presence pulse from the DS1821. This is illustrated in Figure 7. When the

DS1821 sends the presence pulse in response to the reset, it is indicating to the master that it is on the bus

and ready to operate given an appropriate function command.

During the initialization sequence the bus master transmits (T

) the reset pulse by pulling the 1-wire bus

low for a minimum of 480 µs. The bus master then releases the bus and goes into receive mode (R

When the bus is released, the 5k pullup resistor pulls the 1-wire bus high. When the DS1821 detects this

rising edge, it waits 15–60 µs and then transmits a presence pulse by pulling the 1-wire bus low for 60–

240 µs.

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