Rainbow Electronics DS1722 - Manual (Page 5)

DS1722
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CONFIGURATION REGISTER PROGRAMMING
The configuration register is accessed in the DS1722 with the 00h address for reads and the 80h address
for writes. Data is read from or written to the configuration register MSb first for SPI communication and
LSb first for 3-wire communication. The format of the register is illustrated in Figure 2. The effect each
bit has on DS1722 functionality is described below along with the power-up state of the bit. The entire
register is volatile, and thus it will power-up in the default state.
CONFIGURATION/STATUS REGISTER Figure 2
1 1 1 1SHOT R2 R1 R0 SD
MSb LSb
1SHOT = One-shot temperature conversion bit. If the SD bit is "1", (continuous temperature
conversions are not taking place), a "1" written to the 1SHOT bit will cause the DS1722 to perform one
temperature conversion and store the results in the temperature register at addresses 01h (LSB) and 02h
(MSB). The bit will clear itself to "0" upon completion of the temperature conversion. The user has
read/write access to the 1SHOT bit, although writes to this bit will be ignored if the SD bit is a "0",
(continuous conversion mode). The power-up default of the one-shot bit is "0".
R0, R1, R2 = Thermometer resolution bits. Table 4 below defines the resolution of the digital
thermometer, based on the settings of these 3 bits. There is a direct tradeoff between resolution and
conversion time, as depicted in the AC Electrical Characteristics. The user has read/write access to the
R2, R1 and R0 bits and the power-up default state is R2="0", R1="0", and R0="1" (9-bit conversions).
THERMOMETER RESOLUTION CONFIGURATION Table 4
R2 R1 R0 Thermometer Resolution Max Conversion Time
0 0 0 8-bit 0.075s
0 0 1 9-bit 0.15s
0 1 0 10-bit 0.3s
0 1 1 11-bit 0.6s
1 x x 12-bit 1.2s
x=Don’t care.
SD = Shutdown bit. If SD is "0", the DS1722 will continuously perform temperature conversions and
store the last completed result in the temperature register. If SD is changed to a "1", the conversion in
progress will be completed and stored and then the device will revert to a low-power shutdown mode.
The communication port remains active. The user has read/write access to the SD bit and the power-up
default is "1" (shutdown mode).
SERIAL INTERFACE
The DS1722 offers the flexibility to choose between two serial interface modes. The DS1722 can
communicate with the SPI interface or with a standard 3-wire interface. The interface method used is
determined by the SERMODE pin. When this pin is connected to V
DDD
SPI communication is selected.
When this pin is connected to ground, standard 3-wire communication is selected.
SERIAL PERIPHERAL INTERFACE (SPI)
The serial peripheral interface (SPI) is a synchronous bus for address and data transfer. The SPI mode of
serial communication is selected by tying the SERMODE pin to V
DDD
. Four pins are used for the SPI.
The four pins are the SDO (Serial Data Out), SDI (Serial Data In), CE (Chip Enable), and SCLK (Serial
Clock). The DS1722 is the slave device in an SPI application, with the microcontroller being the master.