EM78P809N
8-Bit Microcontroller
4.13 I/O Ports
The I/O registers, Port 6, Port 7, Port 8, and Port 9 are bi-directional tri-state I/O ports.
Each I/O pin can be defined as “input” or “output” pin by the I/O control register (IOC6 ~
IOC9). The I/O registers and I/O control registers are both readable and writable. The
I/O interface circuits for Port 6, Port 7, Port 8, and Port 9 are shown in Fig. 27.
PCRD
P
R
Q
Q
D
CLK
PCWR
C
L
IOD
P
R
PORT
Q
Q
D
PDWR
PDRD
CLK
C
L
0
M
U
X
1
Fig. 28.The I/O Port and I/O Control Register Circuit
4.14 RESET and Wake-up
4.14.1 RESET
A RESET is initiated by one of the following events:
(1) Power-on reset
(2) /RESET pin input “low”
(3) WDT timeout. (if enabled)
The device is kept in a RESET condition for a period of approx. 18ms1 (one oscillator
start-up timer period) after the reset is detected. Once a RESET occurs, the following
functions are performed.
ꢀ
ꢀ
ꢀ
The oscillator starts or is running
The Program Counter (R2) is reset to all “0”.
When power is switched on, the upper 2 bits of R3, the upper 2 bits of R4 and the
bits 6 ~ 4 of R5 are cleared.
ꢀ
All I/O port pins are configured as input mode (high-impedance state).
1 NOTE: VDD = 5V, set up time period = 16.2ms ± 30%
VDD = 3V, set up time period = 19.6ms ± 30%
Product Specification (V1.0) 07.26.2005
• 47
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
