st62t65b STMicroelectronics, st62t65b Datasheet - Page 19

• Manufacturer Part Number: st62t65b
• Description: 8-bit Otp/eprom Mcus With A/d Converter, Auto-reload Timer, Eeprom And Spi
• Manufacturer: STMicroelectronics

CLOCK SYSTEM (Cont’d)
Oscillator Control Registers
Address: DCh — Write only
Bit 7-4. These bits are not used.
Bit 3. Reserved. Cleared at Reset. THIS BIT
MUST BE SET TO 1 BY USER PROGRAM to
achieve lowest power consumption.
Bit 2. Reserved. Must be kept low.
RS1-RS0. These bits select the division ratio of
the Oscillator Divider in order to generate the inter-
nal frequency. The following selctions are availa-
ble:
Figure 9. Clock Circuit Block Diagram
OSCout
7
OSCin
-
RS1
0
0
1
1
-
f
OSC
OSCILLATOR
-
MAIN
-
RS0
0
1
0
1
OSCR
3
f
OSC
OSCR
2
OSCILLATOR
Division Ratio
RS0, RS1
DIVIDE R
RS1
1
2
4
4
RS0
0
Note: Care is required when handling the OSCR
register as some bits are write only. For this rea-
son, it is not allowed to change the OSCR contents
while executing interrupt service routine, as the
service routine cannot save and then restore its
previous content. If it is impossible to avoid the
writing of this register in interrupt service routine,
an image of this register must be saved in a RAM
location, and each time the program writes to
OSCR it must write also to the image register. The
image register must be written first, so if an inter-
rupt occurs between the two instructions the
OSCR is not affected.
ST62T55B ST62T65B/E65B
f
INT
: 12
: 13
: 1
POR
Core
SPI
Timer
Watchdog
ADC
AR Timer
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