DS1821
Nonvolatile write status can be monitored by reading the NVB bit in the status/configuration register:
NVB = 1 – a write to EEPROM memory is in progress, NVB = 0 – nonvolatile memory is idle.
THERMOSTAT MODE
In thermostat mode (T/R¯ = 1), the DS1821 can operate as a standalone thermostat that triggers according
to the TH and TL trip-points programmed while the device was in 1-Wire mode. In thermostat mode the
DS1821 powers-up performing continuous temperature conversions, and the DQ pin acts as the
thermostat output. Detailed operation of the thermostat output is provided in the OPERATION –
STANDALONE THERMOSTAT section of this datasheet.
Communications can be re-established with the DS1821 while it is in thermostat mode by pulling VDD to
0V while the DQ line is held high, and then toggling the DQ line low 16 times as shown in Figure 12.
This temporarily places the DS1821 in 1-Wire mode, allowing microprocessor communication with the
DS1821 via the DQ pin. At this time any I/O function can be performed, such as reading/writing the TH,
TL or configuration registers or reading the temperature register. To return to thermostat mode, the same
procedure can be performed (pulling VDD to 0V while the DQ line is held high, and then clocking the DQ
line 16 times) or the power can be cycled. Note that temporarily putting the DS1821 into 1-Wire mode
does not change the power-up mode of the device; this can only be changed by rewriting the T/R¯ bit in
the status/configuration register. Also note that holding both VDD and DQ low for more than
approximately 10 seconds will cause the DS1821 to be powered down.
OPERATION – MEASURING TEMPERATURE
DS1821 output temperature data is calibrated in degrees centigrade and is stored in two’s complement
format in the 1-byte (8-bit) temperature register (see Figure 3), which the user can access when the
DS1821 is in 1-Wire mode (T/R¯ = 0 in the status/configuration register). The sign bit (S) indicates if the
temperature is positive or negative; for positive numbers S = 0 and for negative numbers S = 1. Table 2
gives examples of digital output data and the corresponding temperature reading. For Fahrenheit
measurements, a lookup table or conversion routine must be used.
The DS1821 can be configured by the user to take continuous temperature measurements (continuous
conversion mode) or single measurements (one-shot mode). The desired configuration can be achieved
by setting the nonvolatile1SHOT bit in the status/configuration register: 1SHOT = 0 – continuous
conversion mode, 1SHOT = 1 – one-shot mode. Note that the 1SHOT setting only controls the operation
of the device in 1-Wire mode; in thermostat mode, continuous temperature conversions are started
automatically at power-up.
In continuous conversion mode, the Start Convert T [EEh] command initiates continuous temperature
conversions, which can be stopped using the Stop Convert T [22h] command. In one-shot mode the Start
Convert T [EEh] command initiates a single temperature conversion after which the DS1821 returns to a
low-power standby state. In this mode, the microprocessor can monitor the DONE bit in the
configuration register to determine when the conversion is complete: DONE = 0 ― conversion in
progress, DONE = 1 ― conversion complete. The DONE bit does not provide conversion status in
continuous conversion mode since measurements are constantly in progress (i.e., DONE will always be
0).
TEMPERATURE, TH and TL REGISTER FORMAT Figure 3
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
S
26
25
24
23
22
21
20
5 of 18
5秒后页面跳转
玻璃管保险丝与陶瓷管保险丝：区别与替代性探讨
PCF8574资料解读：主要参数分析、引脚说明
AD637数据手册解读：主要特性、引脚及其功能解读、电气参数
ADUM1201资料手册解读：参数分析、引脚说明、应用分析
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
技术参数
数据手册
如果您发现信息不准确，
