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System Control Register - CTRL0
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System Control Register - CTRL1
Input/Output Ports
Holtek microcontrollers offer considerable flexibility on
their I/O ports. There are seven I/O pins whose input or
output designation is under user program control and an
additional input pin. Additionally, as there are pull-high
resistor and wake-up software configurations for each
pin, the user is provided with an I/O structure to meet the
needs of a wide range of application possibilities.
Pull-high Resistors
Many product applications require pull-high resistors for
their switch inputs usually requiring the use of an exter-
nal resistor. To eliminate the need for these external re-
sistors, I/O pins PA0~PA6, when configured as an input
have the capability of being connected to an internal
pull-high resistor. These pull-high resistors are
selectable via a register known as PAPU, located in the
Data Memory. The pull-high resistors are implemented
using weak PMOS transistors.
Each device has a single I/O port known as Port A,
which has a corresponding data register known as PA.
This register is mapped to the Data Memory with an ad-
dresses as shown in the Special Purpose Data Memory
table. Seven of these I/O lines can be used for input and
output operations and one line as an input only. For in-
put operation, these ports are non-latching, which
means the inputs must be ready at the T2 rising edge of
instruction ²MOV A,[m]², where m denotes the port ad-
dress. For output operation, all the data is latched and
remains unchanged until the output latch is rewritten.
Rev. 1.10
14
August 13, 2008
HOLTIC [ HOLT INTEGRATED CIRCUITS ]
