HT82B40A datasheet(15/58 Pages) HOLTEK

15 / 58 page

HT82B40R/HT82B40A

Rev. 1.50

February 17, 2011

Pin-shared Functions

The flexibility of the microcontroller range is greatly en-

hanced by the use of pins that have more than one func-

tion. Limited numbers of pins can force serious design

constraints on designers but by supplying pins with

multi-functions, many of these difficulties can be over-

come. For some pins, the chosen function of the

multi-function I/O pins is set by configuration options

while for others the function is set by application pro-

gram control.

· External Timer0 Clock Input

The external timer pin TMR0 is pin-shared with the I/O

pin PA6. To configure this pin to operate as timer input,

the corresponding control bits in the timer control reg-

ister must be correctly set. For applications that do not

require an external timer input, this pin can be used as

a normal I/O pin. Note that if used as a normal I/O pin

the timer mode control bits in the timer control register

must select the timer mode, which has an internal

clock source, to prevent the input pin from interfering

with the timer operation.

· External Timer1 Clock Input

The external timer pin TMR1 is pin-shared with the I/O

pin PA7. To configure this pin to operate as timer input,

the corresponding control bits in the timer control reg-

ister must be correctly set. For applications that do not

require an external timer input, this pin can be used as

a normal I/O pin. Note that if used as a normal I/O pin

the timer mode control bits in the timer control register

must select the timer mode, which has an internal

clock source, to prevent the input pin from interfering

with the timer operation

I/O Pin Structures

The diagram illustrates a generic I/O pin internal struc-

tures. As the exact logical construction of the I/O pin will

differ and as the pin-shared structures are not illustrated

this diagram is 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 initialisation. After a reset, all of the data and

port control register 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 PAC, PBC,

PCC, PDC and PEC port control register, are then pro-

grammed to setup some pins as outputs, these output

pins will have an initial high output value unless the as-

sociated PA, PB, PC, PD and PE port data registers are

first programmed. Selecting which pins are inputs and

which are outputs can be achieved byte-wide by loading

the correct value into the port control register or by pro-

gramming individual bits in the port control register us-

ing the

²SET [m].i² and ²CLR [m].i² instructions. Note

that when using these bit control instructions, 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.

All pins have 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 pins. Single or multiple pins can be setup to

have this function.

V D D / V 3 3 O ( P B )

W a k e - u p O p t i o n

S y s t e m W a k e - u p

R e a d D a t a R e g i s t e r

C K

C o n t r o l B i t

D a t a B u s

W r i t e C o n t r o l R e g i s t e r

C h i p R e s e t

R e a d C o n t r o l R e g i s t e r

W r i t e D a t a R e g i s t e r

D a t a B i t

I / O p i n

W e a k

P u l l - u p

P u l l - H i g h

O p t i o n

Input/Output Ports

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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