HT56RB688_13 datasheet(39/164 Pages) HOLTEK

39 / 164 page

Programming Considerations

Within the user program, one of the first things to consider 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, etc., 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, etc., 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 register or by

programming individual bits in the port control register using 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 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 occur. The device

contains a LCD Driver function, 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 custom LCDs.

Additionally the device also includes LED driver circuitry which can generated the required signals to

drive the COM and SEGMENT signals for LED panels. The device includes a wide range of options to

enable LCD and LED displays of various types to be driven. The table shows the range of options

available across the device range.

Duty

Driver No.

Bias

Bias Type

Wave Type

1/8

´8

1/3, 1/4, 1/5

RA, B

1/16

´16

LCD Selections

LED Duty

LED Driver No.

Static

´1

1/4

´4

1/8

´8

1/12

´12

1/16

´16

LED Selections

HT56RB688

TinyPowerTM A/D type Smart Card OTP MCU

with LCD, DAC, ISO 7816 and USB Interfaces

Rev. 1.10

April 15, 2013

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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