R
EM3027
8.4
Timer function
The 16-bit count down timer can be enabled/disabled by TiOn bit.
The timer input frequency is selected by TD1, TD0 bits according to the following table:
TD1
0
TD0
0
Timer frequency
32 Hz
0
1
8 Hz
1
0
1 Hz
1
1
0.5 Hz
Table 10: Timer Frequency Selection
The timer can run in Zero-Stop or Auto-Reload mode (TROn bit: ‘0’ = Zero-Stop mode, ‘1’ = Auto-Reload mode).
When TROn = ‘0’, then it is possible to read current value of the timer. If TROn = ‘1’, then last written value is read from
cache memory. The value in the cache memory is used as the new value for reloading (Auto-Reload mode).
Frequency selection (TD1, TD0) and mode selection (TROn) can be written only when the timer is stopped (TiOn = ‘0’).
Timer values (TimLow, TimHigh) can be written only when TiOn = ’0’ and TROn = ‘0’.
NOTE: The “Timer Page” can also be used as a general purpose register when the timer function is not used.
8.5
Temperature measurement
The integrated thermometer has a resolution of 1°C.
The thermometer is disabled when ThEn = ’0’ and enabled when ThEn = ’1’. By default, the thermometer is enabled.
Thermometer period is selectable by ThPer bit according to the table below:
ThPer
Period in Seconds
0
1
1 s
16 s
Table 11: Thermometer Period
The thermometer is automatically disabled when VLOW1 status bit is at ‘1’.
When the thermometer is disabled (ThEn = ’0’), the Temp register can be written. Temp register uses a cache memory to
keep stable value during a whole transaction (read/write).
8.6
Frequency compensation
There is a frequency compensation unit (FCU) inside EM3027. FCU compensates quartz crystal native frequency in
dependency on actual compensation value (COMP_val).
FCU is always running.
During chip power-up, if ThEn = ’1’ and VLOW1 = ‘0’ temperature measurement is enabled and COMP_val is computed.
Otherwise, COMP_val is set to 0ppm.
In Normal mode, new compensation value is computed each 32 seconds. The only exception is when ThEn = ‘1’ and
VLOW1 = ‘1’. In this case, temperature measurement and COMP_val computation are blocked and FCU uses the last
computed compensation value.
For the evaluation of COMP_val, actual content of Temp register (0x20) is used. The compensation value is computed
according to the equation described in paragraph 4.3.
Content of Temp register is updated either after a temperature measurement (when ThEn = '1' and VLOW1 = '0') or after
Temp register write transaction (when ThEn = '0'). After power-up content of Temp register is undefined.
If thermometer is disabled (ThEn = '0') user is advised to periodically update Temp register with actual ambient temperature
in order to have correct input data for COMP_val computation.
Copyright © 2009, EM Microelectronic-Marin SA
12/09 – rev D
www.emmicroelectronic.com
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