ST6255B View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
ST6255B
STMicroelectronics
'ST6255B' PDF : 74 Pages View PDF
ST62T55B ST62T65B/E65B
CLOCK SYSTEM (Cont’d)
Oscillator Control Registers
Address: DCh — Write only
7
0
-
-
-
-
OSCR OSCR
3
2
RS1
RS0
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:
RS1
RS0
Division Ratio
0
0
1
0
1
2
1
0
4
1
1
4
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.
Figure 9. Clock Circuit Block Diagram
fOSC
OSCin
fOSC
MAIN
OSCILLATOR
OSCILLATOR
DIVIDE R
POR
Core
: 13
SPI
Timer
fINT
Watchdog
: 12
ADC
OSCout
RS0, RS1
:1
AR Timer
19/74
19
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