Supply, reset and clock management
ST7L34, ST7L35, ST7L38, ST7L39
Doc ID 11928 Rev 7
7
Supply, reset and clock management
The device includes a range of utility features for securing the application in critical
situations (for example, in case of a power brown-out) and reducing the number of external
components.
Main features
●
Clock management
–
1 MHz internal RC oscillator (enabled by option byte)
–
1 to 16 MHz or 32 kHz external crystal/ceramic resonator (selected by option byte)
–
External clock input (enabled by option byte)
–
PLL for multiplying the frequency by 8(enabled by option byte)
●
Reset sequence manager (RSM)
●
System integrity management (SI)
–
Main supply low voltage detection (LVD)with reset generation (enabled by option
byte)
–
Auxiliary voltage detector (AVD) with interrupt capability for monitoring the main
supply (enabled by option byte)
7.1
Internal RC oscillator adjustment
The device contains an internal RC oscillator with high accuracy for a given device,
temperature and voltage. It must be calibrated to obtain the frequency required in the
application. This is done by the software writing an 8-bit calibration value in the RCCR (RC
control register) and in the bits [6:5] in the SICSR (SI control status register).
Whenever the microcontroller is reset, the RCCR returns to its default value (FFh), that is,
each time the device is reset, the calibration value must be loaded in the RCCR. Predefined
calibration values are stored in EEPROM for 3.3 V and 5 V VDD supply voltages at 25°C, as
Table 7.
RCCR calibration registers
RCCR
Conditions
ST7L3 addresses
RCCRH0
VDD = 5 V
TA = 25°C
fRC = 1 MHz
(1)
1.
RCCR0 and RCCR1 calibrated within these conditions in order to reach RC accuracy as mentioned in
DEE0h(2) (CR[9:2] bits)
2.
DEE0h, DEE1h, DEE2h and DEE3h addresses are located in a reserved area but are special bytes
containing also the RC calibration values which are read-accessible only in user mode. If all the EEPROM
data or Flash space (including the RC calibration values locations) has been erased (after the readout
protection removal), then the RC calibration values can still be obtained through these four addresses.
For compatibility reasons with the SICSR register, CR[1:0] bits are stored in the fifth and sixth positions of
DEE1 and DEE3 addresses.
RCCRL0
RCCRH1
VDD = 3.3 V
TA = 25°C
RCCRL1