DS1620SSLASHT&R datasheet(6/12 Pages) MAXIM

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DS1620

1SHOT = One–Shot Mode. If 1SHOT is 1, the DS1620 will perform one temperature conversion upon

reception of the Start Convert T protocol. If 1SHOT is 0, the DS1620 will continuously perform

temperature conversion. This bit is stored in nonvolatile E2 memory, capable of at least 50,000 writes. The

DS1620 is shipped with 1SHOT=0.

For typical thermostat operation, the DS1620 will operate in continuous mode. However, for applications

where only one reading is needed at certain times or to conserve power, the one–shot mode may be used.

Note that the thermostat outputs (THIGH, TLOW, TCOM) will remain in the state they were in after the last

valid temperature conversion cycle when operating in one–shot mode.

OPERATION IN STAND-ALONE MODE

In applications where the DS1620 is used as a simple thermostat, no CPU is required. Since the

temperature limits are nonvolatile, the DS1620 can be programmed prior to insertion in the system. In

order to facilitate operation without a CPU, the CLK/ CONV pin (pin 2) can be used to initiate

conversions. Note that the CPU bit must be set to 0 in the configuration register to use this mode of

operation. Whether CPU=0 or 1, the 3–wire port is active. Setting CPU=1 disables the stand–alone mode.

To use the CLK/ CONV pin to initiate conversions, RST must be low and CLK/ CONV must be high. If

CLK/ CONV is driven low and then brought high in less than 10 ms, one temperature conversion will be

performed and then the DS1620 will return to an idle state. If CLK/ CONV is driven low and remains low,

continuous conversions will take place until CLK/ CONV is brought high again. With the CPU bit set to 0,

the CLK/ CONV will override the 1SHOT bit if it is equal to 1. This means that even if the part is set for

one–shot mode, driving CLK/ CONV low will initiate conversions.

3-WIRE COMMUNICATIONS

The 3–wire bus is comprised of three signals. These are the RST (reset) signal, the CLK (clock) signal,

and the DQ (data) signal. All data transfers are initiated by driving the RST input high. Driving the RST

input low terminates communication. (See Figures 4 and 5.) A clock cycle is a sequence of a falling edge

followed by a rising edge. For data inputs, the data must be valid during the rising edge of a clock cycle.

Data bits are output on the falling edge of the clock and remain valid through the rising edge.

When reading data from the DS1620, the DQ pin goes to a high-impedance state while the clock is high.

Taking RST low will terminate any communication and cause the DQ pin to go to a high-impedance

state.

Data over the 3–wire interface is communicated LSB first. The command set for the 3–wire interface as

shown in Table 4 is as follows.

Read Temperature [AAh]

This command reads the contents of the register which contains the last temperature conversion result.

The next nine clock cycles will output the contents of this register.

Write TH [01h]

This command writes to the TH (HIGH TEMPERATURE) register. After issuing this command the next

nine clock cycles clock in the 9–bit temperature limit which will set the threshold for operation of the

THIGH output.

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