ht82k68e-l Holtek Semiconductor Inc., ht82k68e-l Datasheet - Page 12

• Manufacturer Part Number: ht82k68e-l
• Description: Ht82k68e-l/ht82k68a-l -- Multimedia Keyboard Encoder 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

Reset
There are three ways in which a reset can occur:
The WDT time-out during HALT is different from other
chip reset conditions, since it can perform a warm reset
that just resets the program counter and stack pointer,
leaving the other circuits to remain in their original state.
Some registers remain unchanged during other reset
conditions. Most registers are reset to the initial condi-
tion when the reset conditions are met. By examining
the PDF and TO flags, the program can distinguish be-
tween different chip resets .
Note: u means unchanged
To guarantee that the system oscillator has started and
stabilized, the SST (System Start-up Timer) provides an
extra-delay of 1024 system clock pulses when the sys-
tem powers up or when it awakes from the HALT state.
When a system power-up occurs, the SST delay is
added during the reset period. But when the reset co-
mes from the RESET pin, the SST delay is disabled.
Any wake-up from HALT will enable the SST delay.
The functional unit chip reset status is shown below.
Rev. 1.10
Program Counter
Prescaler
WDT
Timer counter
Input/output ports
Stack Pointer
RESET reset during normal operation
RESET reset during HALT
WDT time-out reset during normal operation
TO
0
u
0
1
1
Bit No.
0~3
4
5
6
7
PDF
0
u
0
u
1
RESET reset during power-up
RESET reset during normal operation
RESET wake-up HALT
WDT time-out during normal operation
WDT wake-up HALT
Label
TON
TM0
TM1
000H
Clear
Clear. After master reset,
WDT begins counting
Off
Input mode
Points to the top of the stack
RESET Conditions
Unused bit, read as "0"
To enable/disable timer counting (0= disabled; 1= enabled)
Unused bit, read as "0"
10= Timer mode (internal clock)
TMRC (0EH) Register
12
Timer Counter
A timer counter (TMR) is implemented in the
microcontroller. The timer counter contains an 8-bit
programmable count-up counter and the clock may
come from the system clock divided by 4.
Using the internal instruction clock, there is only one ref-
erence time-base.
There are two registers related to the timer counter;
TMR ([0DH]), TMRC ([0EH]). Two physical registers are
mapped to TMR location; writing TMR makes the start-
ing value be placed in the timer counter preload register
and reading TMR gets the contents of the timer counter.
The TMRC is a timer counter control register, which de-
fines some options.
Function
HT82K68E-L/HT82K68A-L
Reset Configuration
Reset Timing Chart
Reset Circuit
April 2, 2008