HMS87C5216 Datasheet, PDF (66/76 Pages) List of Unclassifed Manufacturers – CMOS SINGLE-CHIP 8-BIT MICROCONTROLLER FOR UR(Universal Remocon) & WIRELESS KEYBOARD

HMS87C5216
17. RESET FUNCTION
17.1 EXTERNAL RESET
The RESET pin should be held at low for at least 2machine cycles
with the power supply voltage within the operating voltage range
and must be connected 0.1uF capacitor for stable system initial-
ization. The RESET pin contains a Schmitt trigger with an inter-
nal pull-up resistor.
RESET
0.1 uF Capacitor
Figure 17-1
17.2 POWER ON RESET
Power On Reset circuit automatically detects the rise of power
voltage (the rising time should be within 50ms) the power volt-
age reaches a certain level, RESET terminal is maintained at
°»L°» Level until a crystal ceramic oscillator oscillates stably.
After power applies and starting of oscillation, this reset state is
maintained for about oscillation cycle of 219 (about 65.5ms : at
4MHz).The execution of built-in Power On Reset circuit is as fol-
lows :
(1) Latch the pulse from Power On Detection Pulse Generator cir-
cuit, and reset Prescaler, B.I.T and B.I.T Overflow detection cir-
cuit.
(2) Once B.I.T Overflow detection circuit is reset. Then, Prescal-
er starts to count.
(3) Prescaler output is inputted into B.I.T and PS10 of Prescaler
output is automatically selected. If overflow of B.I.T is detected,
Overflow detection circuit is set.
(4) Reset circuit generates maximum period of reset pulse from
Prescaler and B.I.T.
Internal IC
VDD
RESET
0.1uF
Internal Reset
Power On DET
Pulse GEN.
XTAL
OSC.
VSS
CLR
Prescaler
PS10
CLR
Basic Interval
Tiemr
MSB
CLR
Basic Interval
Tiemr
Figure 17-2 Block Diagram of Power On Reset Circuit
Note: Notice ; When Power On Reset, oscillator stabiliza-
tion time doesn`t include OSC. Start time.
SEP. 2004 Ver 1.01