HMS87C1808B Datasheet, PDF (77/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
19. RESET
The reset input is the RESET pin, which is the input to a Schmitt
Trigger. A reset is 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 19-1 .
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
ADDRESS
BUS
DATA
BUS
1234567
?
??
?
FFFE FFFF Start
?
Stabilizing Time
t_ST = 64mS at 4MHz
? ? ? FE ADL ADH OP
RESET Process Step
MAIN PROGRAM
Figure 19-1 Timing Diagram after RESET
A power-up example where RESET is connected to external reset
circuit is shown in Figure 19-2 . V_DD is allowed to rise and stabi-
lize before bringing RESET high. The chip will actually come out
of reset and start the Basic Interval Timer after RESET goes high.
V_DD
RESET
INTERNAL
RESET
Stabilizing Time
Basic Interval Timer Start
Figure 19-2 Time-out Sequence On Power-up
Note: When the device starts normal operation (exits the
reset condition), device operating parameters (voltage, fre-
quency, temperature, etc.) must be meet to ensure opera-
tion. If these conditions are not met, the device must be
held in reset until the operating conditions are met
SEP. 2004 Ver 1.03
73