HT95R34 datasheet(17/59 Pages) HOLTEK

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HT95R34

Rev. 1.10

February 18, 2009

Input/Output Ports

Holtek microcontrollers offer considerable flexibility on

their I/O ports. With the input or output designation of ev-

ery pin fully under user program control, pull-high op-

tions for all ports and wake-up options on certain pins,

the user is provided with an I/O structure to meet the

needs of a wide range of application possibilities. The

device provides 26 bidirectional input/output lines la-

beled with port names PA, PC, PD and PE. These I/O

ports are mapped to the Data Memory with specific ad-

dresses as shown in the Special Purpose Data Memory

table. All of these I/O ports can be used for input and

output operations. For input 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 address. For output operation, all the

data is latched and remains unchanged until the output

latch is rewritten.

Unlike other port lines, PC2 and PC3 are supplied as

NMOS output-only lines. They have neither pull high op-

tion nor port control bit.

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, all I/O pins, when configured as an input have

the capability of being connected to an internal pull-high

resistor. These pull-high resistors are selectable via

configuration options and are implemented using a

weak PMOS transistor.

Port A Wake-up

Each device has a HALT instruction enabling the

microcontroller to enter a Power Down Mode and pre-

serve power, a feature that is important for battery and

other low-power applications. Various methods exist to

wake-up the microcontroller, one of which is to change

the logic condition on one of the Port A pins from high to

low. After a

²HALT² instruction forces the microcontroller

into entering the Power Down mode, the device will re-

main idle or in a low-power state until the logic condition

of the selected wake-up pin on Port A changes from high

to low. This function is especially suitable for applica-

tions that can be woken up via external switches. Note

that each pin on Port A can be selected individually to

have this wake-up feature.

I/O Port Control Registers

Each I/O port has its own control register PAC, PCC,

PDC and PEC, to control the input/output configuration.

with this control register, each CMOS output or input

with or without pull-high resistor structures can be re-

configured dynamically under software control. Each pin

of the I/O ports is directly mapped to a bit in its associ-

ated port control register. For the I/O pin to function as

an input, the corresponding bit of the control register

must be written as a

²1². This will then allow the logic

state of the input pin to be directly read by instructions.

When the corresponding bit of the control register is

written as a

²0², the I/O pin will be setup as a CMOS out-

put. If the pin is currently setup as an output, instructions

can still be used to read the output register. However, it

should be noted that the program will in fact only read

the status of the output data latch and not the actual

logic status of the output pin.

I/O Pin Structures

The following diagrams illustrate the I/O pin internal

structures. As the exact logical construction of the I/O

pin may differ from these drawings, they are supplied as

a guide only to assist with the functional understanding

of the I/O pins.

Programming Considerations

Within the user program, one of the first things to con-

sider is port initialization. After a reset, all of the I/O data

and port control registers will be set high. This means

that all I/O pins will default to an input state, the level of

which depends on the other connected circuitry and

whether pull-high options have been selected. If the port

control registers, PAC, PCC, PDC and PEC, are then

programmed to setup some pins as outputs, these out-

put pins will have an initial high output value unless the

associated port data registers, PA, PC, PD and PE, are

first programmed. Selecting which pins are inputs and

which are outputs can be achieved byte-wide by loading

the correct values into the appropriate port control regis-

ter or by programming individual bits in the port control

²SET [m].i² and ²CLR [m].i² instruc-

tions. Note that when using these bit control instruc-

tions, a read-modify-write operation takes place. The

microcontroller must first read in the data on the entire

port, modify it to the required new bit values and then re-

write this data back to the output ports.

Port A has the additional capability of providing wake-up

functions. When the device is in the Power Down Mode,

various methods are available to wake the device up.

One of these is a high to low transition of any of the Port

A pins. Single or multiple pins on Port A can be setup to

have this function.

T 1

T 2

T 3

T 4

T 1

T 2

T 3

T 4

W r i t e t o P o r t

R e a d f r o m P o r t

S y s t e m C l o c k

P o r t D a t a

Read/Write Timing

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