HT48R03 Holtek Semiconductor, HT48R03 Datasheet - Page 12

• Manufacturer Part Number: HT48R03
• Description: (HT48R01 - HT48R03) 10-Pin MSOP I/O Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

If the configuration options select the IRC+RTC, the de-
vice supports two kinds of system clock. When com-
bined with the Power-down function, it forms three
operation modes. The two kinds of system clock are in-
ternal RC oscillator or RTC OSC (32768Hz) which is se-
lected by the CTRL register CLKMOD bit. The three
operation modes are named as Normal, Slow, or Idle
mode. The following tables shows their relationship.
If an RC oscillator is used, an external resistor between
OSC1 and VDD is required whose resistance must
range from 24kW to 1.5MW. The RC oscillator provides
the most cost effective solution. The frequency of oscil-
lation may vary with VDD, temperatures and the chip it-
self due to process variations. It is, therefore, not
suitable for timing sensitive operations where an accu-
rate 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, and no other external
components are demanded. Instead of a crystal, a reso-
nator can also be connected between OSC1 and OSC2
to obtain a frequency reference, but two external capaci-
tors connected to OSC1 and OSC2 are required. If an
internal RC oscillator is used, OSC1 and OSC2 can be
selected as general I/O lines or as a 32768Hz crystal
(RTC) oscillator. The frequencies of internal oscillator
can be 12MHz, 8MHz and 4MHz which is selected by
configuration options.
The WDT oscillator is a free running on-chip RC oscilla-
tor, and no external components are required. Even if
the system enters the power down mode, the system
clock is stopped, but the WDT oscillator still works with a
period of approximately 65ms at 5V. The WDT oscillator
can be disabled by configuration options to conserve
power.
Rev. 1.00
During run state (HALT not execute)
During run state (HALT execute)
HALT Instruction
CLKMOD
0
1
x
System Oscillator
RC Oscillator
12
On
Off
Off
Watchdog Timer - WDT
The WDT clock source may come from a dedicated RC
oscillator (WDT oscillator), RTC clock or instruction
clock (system clock divided by 4) which is determined by
option. This timer is designed to prevent a software mal-
function or sequence from jumping to an unknown loca-
tion with unpredictable results. The Watchdog Timer can
be disabled by options. If the Watchdog Timer is dis-
abled, all the executions related to the WDT result in no
operation. The RTC clock is enabled only in the internal
RC+RTC mode.
The WDT clock (f
counter to give longer watchdog time-outs.
Once the internal WDT oscillator (RC oscillator with a
period of 65ms at 5V normally) is selected, it is first di-
vided by 256 (8-stage) to get the nominal time-out pe-
riod of approximately 17ms at 5V. This time-out period
may vary with temperatures, VDD and process varia-
tions. By invoking the WDT prescaler, longer time-out
periods can be realized. Writing data to WS2, WS1,
WS0 (bit 2,1,0 of the WDTS) can give different time-out
periods. If WS2, WS1 and WS0 are all equal to ²1², the
division ratio is up to 1:128, and the maximum time-out
period is 2.1s at 5V seconds. If the WDT oscillator is dis-
abled, the WDT clock may still come from the instruction
clock and operate in the same manner except that in the
HALT state the WDT may stop counting and lose its pro-
tecting purpose. In this situation the logic can only be re-
started by external logic.
If the device operates in a noisy environment, using the
on-chip RC oscillator (WDT OSC) is strongly recom-
mended, since the HALT will stop the system clock.
Bit No.
0~2
3~7
HT48R01/HT48R02/HT48R03
32768Hz
On
On
On
WS0~
WS2
Label
¾
WDTS (09H) Register
S
) is further divided by an internal
WDT prescaler rate select
Unused bit, read as ²0²
System Clock
RC oscillator
32768Hz
HALT
Function
December 20, 2006
Normal
Mode
Slow
Idle