Elan EM78P156EL Manual page 15

4.4 I/O Ports
The I/O registers, both Port 5 and Port 6, are bi-directional tri-state I/O ports. Port 6 can be pulled high
internally by software. In addition, Port 6 can also have open-drain output by software. Input status
change interrupt (or wake-up) function on Port 6. P50 ~ P52 and P60 ~ P63 pins can be pulled down by
software. Each I/O pin can be defined as "input" or "output" pin by the I/O control register (IOC5 ~ IOC6).
P50~P51 are the R -option pins enabled by setting the ROC bit in the IOCE register to 1. When the
R-option function is used, it is recommended that P50~P51 are used as output pins. When R-option is in
enable state, P50~P51 must be programmed as input pins. Under R -option mode, the current/power
consumption by Rex should be taken into the consideration to promote energy conservation.
The I/O registers and I/O control registers are both readable and writable. The I/O interface circuits for
Port 5 and Port 6 are shown in the following Figures 6, 7(a), 7(b), and Figure 8.
PORT
This specification is subject to change without prior notice.
0
M
U
1
X
NOTE: Pull-down is not shown in the figure.
Fig. 6 The Circuit of I/O Port and I/O Control Register for Port 5
PCRD
P
Q
D
R
PCWR
CLK
_
C
Q
L
P
Q D
R
CLK PDWR
_
C
Q
L
PDRD
15
EM78P156EL
OTP ROM
IOD
2002/04/19