User guide

18
SmartBook for Renesas R8C/Tiny Microcontrollers
www.MightyMicons.com
The R8C/Tiny controllers sport a versatile reset
facility to keep the controller working in the stable
conditions in spite of variations in the operating
voltage along with a dedicated watchdog timer. These
devices also contain a power on reset function without
any external device to bring up the hardware in an
orderly manner. Basically, this function is built using a
voltage detection circuit which compares the operating
voltage with a reference voltage, Vdet, of 3.8V. Whenever
the operating voltage crosses this Vdet, the voltage detector
generates an interrupt and also the reset condition can be
activated. The voltage detector can generate interrupts for both rising
and falling operating voltages. Apart from all these hardware facilities,
the controller can also be reset by software.
The R8C/Tiny devices have three types of resets: A Hardware Reset, Software
Reset and a Watchdog Timer Reset. Further, the hardware reset represents
Hardware Reset 1, Hardware Reset 2 and Power on Reset. Hardware Reset 1 is
the simple one, forcing the device into reset by applying a pulse signal at the
RESET pin with an active low level for atleast 500 microseconds. When this
RESET pin is in low level, pins of the controller are initialized. When the voltage
level is increased from low to high level, the CPU and SFR are initialized and the
program is executed starting from the address indicated by the Reset Vector
(FFFCH). After reset, all the registers become zero and the PC gets the reset
vector. Also all the ports are initialized for the inputs.
2.10 Hardware Reset 2:
The operation of this hardware reset depends upon the device operating voltage.
The device’s built in voltage detector circuit monitors the supply voltage at the
Vcc pin. When this voltage detector function is initialized (VC27 bit in the Voltage
Detection Register VCR2 is set to 1) the device gets ready to activate this hardware
reset.
When the supply voltage at the Vcc pin rises to Vdet or more, the pins, CPU and
SFR are initialized and the counting of low speed on chip oscillator starts. When
the counter counts upto 32 clocks (of the onchip low speed ring oscillator), the
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After reset, all the
registers become zero
and the PC gets the reset
vector. Also all the
ports are initialized
for the inputs. When the counter counts
upto 32 clocks (of the onchip low speed
ring oscillator), the internal reset
condition is exited and the
program is executed beginning
with the address indicated
by the reset vector
FFFCH.