HT56R67 datasheet(27/104 Pages) HOLTEK

27 / 104 page

HT56R67/HT56R668/HT56C668/HT56R678/HT56C678/HT56R688

Rev. 1.20

February 22, 2010

Programming Considerations

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

sider is port initialisation. 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 selections have been chosen. If the

port control registers, PAC, PBC, PCC and PDC, are

then programmed to setup some pins as outputs, these

output pins will have an initial high output value unless

the associated port data registers, PA, PB, PC and PD,

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 con-

trol register or by programming individual bits in the port

control register using the

²SET [m].i² and ²CLR [m].i² in-

structions. Note that when using these bit control in-

structions, a read-modify-write operation takes place.

The microcontroller must first read in the data on the en-

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

rewrite 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.

LCD and LED Driver

For large volume applications, which incorporate an

LCD in their design, the use of a custom display rather

than a more expensive character based display reduces

costs significantly. However, the corresponding COM

and SEG signals required, which vary in both amplitude

and time, to drive such a custom display require many

special considerations for proper LCD operation to oc-

cur. These devices all contain an LCD Driver function,

which with their internal LCD signal generating circuitry

and various options, will automatically generate these

time and amplitude varying signals to provide a means

of direct driving and easy interfacing to a range of cus-

tom LCDs.

Additionally some of the devices also include LED driver

circuitry which can generated the required signals to

drive the COM and SEGMENT signals for LED panels.

All device include a wide range of options to enable LCD

and LED displays of various types to be driven. The ta-

ble shows the range of options available across the de-

vice range.

Part No.

Duty

Driver

No.

Bias

Type

Wave

Type

HT56R67

1/2

´2

1/2

1/3

´3

1/4

´4

HT56R668

HT56C668

HT56R678

HT56C678

HT56R688

1/8

´16

1/3

1/4

1/5

1/16

´8

LCD Selections

Note:

The HT56R67 devices do not have an LED

driver function.

Device

LED Duty

LED Driver No.

HT56R668

HT56C668

HT56R678

HT56C678

HT56R688

Static

´1

1/4

´4

1/8

´8

1/12

´12

1/16

´16

LED Selections

Note:

The and HT56R67 devices do not have an LED

driver 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

HT56R67 Datasheet(PDF) 27 Page - Holtek Semiconductor Inc

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