HMS87C13042A Datasheet, PDF (69/88 Pages) Hynix Semiconductor – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C130XA/120XA/110XA
18. RESET
The reset input is the RESET pin, which is the input to a
Schmitt Trigger. A reset in accomplished by holding the
RESET pin low for at least 8 oscillator periods, while the
oscillator running. After reset, 64ms (at 4 MHz) add with
7 oscillator periods are required to start execution as shown
in Figure 18-1.
Internal RAM is not affected by reset. When V_DD is turned
on, the RAM content is indeterminate. Therefore, this
RAM should be initialized before reading or testing it.
Initial state of each register is shown as Table 8-1.
Oscillator
(X_IN pin)
RESET
1234567
ADDRESS
BUS
DATA
BUS
?
??
?
FFFE FFFF Start
?
Stabilizing Time
t_ST = 64mS at 4MHz
? ? ? FE ADL ADH OP
RESET Process Step
MAIN PROGRAM
Figure 18-1 Timing Diagram after RESET
• Power-On Reset (POR)
The HMS87C130XA incorporates on-chip Power-On Re-
set (POR) circuitry which provides an internal chip reset
for most power-up situations. To use this feature, the user
merely ties the RESET pin to V_DD and setting the POREN
bit of CONFIG register ( refer to Figure 20-1).
A Power-on Reset pulse is generated on-chip when V_DD
rise is detected approximately 1V. To take an advantage of
the Power-on Reset, just tie the RESET pin directly ( or
through the resistor ) to V_DD.
V_DD
RESET
INTERNAL RESET
Basic Interval Timer Start
Figure 18-2 Time-out Sequence On Power-up (RESET Tied To V_DD): Fast V_DD Rise Time
A power-up example where RESET is not tied to V_DD is
shown in Figure 18-2. V_DD is allowed to rise and stabilize
before bringing RESET high. The chip will actually come
out of reset and start the Basic Interval Timer after RESET
goes high.
In Figure 18-3, the on-chip Power-On Reset feature is be-
ing used (RESET and V_DD are tied together). The V_DD is
stable before the Basic interval timer times out and there is
no problem in getting a proper reset. However, Figure 18-
4 depicts a problem situation where V_DD rises too slowly.
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Apr. 2001 ver 1.0