HT45R34 Holtek Semiconductor, HT45R34 Datasheet - Page 18

• Manufacturer Part Number: HT45R34
• Description: C/R to F Type 8-Bit OTP MCU
• Manufacturer: Holtek Semiconductor

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Input/Output Ports
There are 8 bidirectional input/output lines in the
microcontroller, all located within port PA. All of these I/O
ports can be used for input and output operations. For
input operation, these ports are non-latching, that is, the
inputs must be ready at the T2 rising edge of the MOV
A,[m] instruction. For output operation, all the data is
latched and remains unchanged until the output latch is re-
written.
Each I/O line has its own control register, known as
PAC, to control the input/output configuration. With this
control register, the pin status is either a CMOS output
or a Schmitt trigger input, but can be reconfigured dy-
namically, under software control. To function as an in-
put, the corresponding bit in the control register must be
written with a 1 . The input source also depends on the
control register. If the control register bit is 1 , the input will
read the pad state. If the control register bit is 0 , the con-
tents of the latches will move to the internal bus. The latter
is possible in the read-modify-write instruction.
When setup as an output the output types are CMOS.
After a device reset, the I/O ports will be initially all setup
as inputs, and will therefore be in a high state if the
configuration options have selected pull-high resistors,
otherwise they will be in a floating condition. Each bit of
these input/output latches can be set or cleared by the
Some instructions first input data and then follow the
output operations. For example, SET [m].i , CLR
[m].i , CPL [m] , CPLA [m] read the entire port states
into the CPU, execute the defined operations
Rev. 1.20
SET [m].i and CLR [m].i instructions.
Input/Output Ports
18
(bit-operation), and then write the results back to the
latches or the accumulator.
Each line of port A has the capability of waking-up the de-
vice.
Each line of port A has a pull-high option. Once the
pull-high option is selected, the I/O line will have a
pull-high resistor connected. Otherwise, the pull-high re-
sistors are absent. It should be noted that a
non-pull-high I/O line operating in an input mode will be
in a floating state.
The PA0, PA1 and PA2 are pin-shared with INT0, INT1
and TMR pins, respectively.
It is recommended that unused or not bonded out I/O
lines should be set as output pins using software in-
struction to avoid consuming power under input floating
state.
Low Voltage Reset - LVR
The microcontroller provides a low voltage reset circuit
in order to monitor the supply voltage of the device. If the
supply voltage of the device is within the range
0.9V~V
will automatically reset the device internally.
The LVR includes the following specifications:
The low voltage (0.9V~V
nal state for longer than t
does not exceed t
perform a reset function.
The LVR uses an OR function with the external RES
signal to perform a chip reset.
LVR
, such as when changing a battery, the LVR
LVR
, the LVR will ignore it and will not
LVR
LVR
) has to remain in its origi-
. If the low voltage state
October 15, 2007
HT45R34