HT45R36 Holtek Semiconductor, HT45R36 Datasheet - Page 11

• Manufacturer Part Number: HT45R36
• Description: C/R to F Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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Oscillator Configuration
There are two oscillator circuits in the microcontroller.
Both are designed for system clocks, namely the RC os-
cillator and the Crystal oscillator, the choice of which is
determined by a configuration option. When the device
enters the Power Down Mode, the system oscillator will
stop running and will ignore external signals to conserve
power.
If an RC oscillator is used, an external resistor between
OSC1 and VDD is required to produce oscillation. The
resistance must range from 24k
clock, divided by 4, is available on OSC2, which can be
used to synchronize external logic. The RC oscillator
provides the most cost effective solution, however, the
frequency of oscillation may vary with VDD, tempera-
tures and the device itself due to process variations. It is,
therefore, not suitable for timing sensitive operations
where an accurate oscillator frequency is desired.
If the Crystal oscillator is used, a crystal across OSC1
and OSC2 is needed to provide the feedback and phase
shift required for the oscillator. No other external compo-
nents are required. Instead of a crystal, a resonator can
Rev. 1.00
1~3, 5~7
Bit No.
Bit No.
0
1
2
3
4
5
6
7
0
4
ERCOCI Controls the external RC oscillation converter interrupt (1= enabled; 0= disabled)
RCOCF External RC oscillation converter request flag (1= active; 0= inactive)
Label
Label
EEI0
EEI1
EIF0
EIF1
EMI
ETI
TF
System Oscillator
Controls the master (global) interrupt (1= enabled; 0= disabled)
Controls the external interrupt 0 (1= enabled; 0= disabled)
Controls the external interrupt 1 (1= enabled; 0= disabled)
Controls the Timer/Event Counter interrupt (1= enabled; 0= disabled)
External interrupt 0 request flag (1= active; 0= inactive)
External interrupt 1 request flag (1= active; 0= inactive)
Internal Timer/Event Counter request flag (1= active; 0= inactive)
Unused bit, read as 0
Unused bit, read as 0
to 1M . The system
INTC0 (0BH) Register
INTC1 (1EH) Register
11
also be connected between OSC1 and OSC2 to get a
frequency reference, but two external capacitors con-
nected between OSC1, OSC2 and ground are required,
if the oscillator frequency is less than 1MHz.
The WDT oscillator is a free running on-chip RC oscilla-
tor which requires no external components. Even if the
system enters the Power Down Mode, where the sys-
tem clock is stopped, the WDT oscillator will continue to
operate with a period of approximately 65 s at 5V. The
WDT oscillator can be disabled by a configuration option
to conserve power.
Watchdog Timer - WDT
The WDT clock can be sourced from its own dedicated
internal oscillator (WDT oscillator), or from the or in-
struction clock, which is the system clock divided by 4.
The choice is determined via a configuration option. The
WDT timer is designed to prevent a software malfunc-
tion or sequence from jumping to an unknown location
with unpredictable results. The Watchdog Timer can be
disabled by a configuration option. If the Watchdog
Timer is disabled, any executions related to the WDT re-
sult in no operation.
The WDT clock source is first divided by 256. If the inter-
nal WDT oscillator is used ,this gives a nominal time-out
period of approximately 17ms at 5V. This time-out pe-
riod may vary with temperatures, VDD and process vari-
ations. By using the WDT prescaler, longer time-out
periods can be realised. Writing data to the WS2, WS1,
WS0 bits in the WDTS register, can give different
time-out periods. If WS2, WS1, and WS0 are all equal to
1, the division ratio will be 1:128, and the maximum
time-out period will be 2.1s at 5V. If the internal WDT os-
Function
Function
September 28, 2006
HT45R36