Touch Key LCD Display Card Reference Design...LCD displays “-----” LCD shifts to the right and...

Touch Key LCD Display Card Reference Design

WAS-19C1EN V1.00 1 / 11 September 25, 2020


D/N: WAS-19C1EN

Introduction

Smart cards integrated with a password display function are called display cards. The display card

is turned on by entering a PIN code. This PIN code is then used along with the entered transaction

information to calculate an SHA dynamic password (TOTP) which is then displayed on an LCD

screen. This improves the security of e-banking login and reduces the possibility of transaction loss

due to phishing websites. The display card has an integrated paper battery with a capacity of

15mAH which can provide a guaranteed battery life of 3~5 years.

Figure 1

Application Areas

e-Banking, touch key LCD display cards, ultra-low power touch key + LCD products.

Solution Features

1. Ultra-low standby current: the product 1-key wake-up standby current is 130nA@3V.

The BS67F2563 includes a low frequency 32768Hz crystal oscillator circuit. Its extremely

low oscillation current allows a 1-key standby current of 130nA@3V(Typ.) for the product. It

can be used for accurate time counting combined with an internal Time Base counter.

2. High level of functional integration: only a few external components are required.

The BS67F2563 includes up to 20 internal capacitive touch keys with the touch sensitivity

adjustable by firmware to fit into different materials or media. The integrated C-type LCD

driver reduces power consumption when the LCD display is being used.



3. High contrast LCD display: internal reference voltage.

The BS67F2563 includes an internal reference voltage boost function, which can be used with

the LVD to detect the battery voltage to avoid LCD grayscale display under low battery

voltage conditions.

Functional Description

The Holtek touch key LCD display card solution is mainly composed of the BS67F2563 master

MCU, a 32768Hz crystal oscillator with CL≤7pF as specified, an LCD power supply circuit and a

6-digit segment LCD panel and also reserved SIM card contact points. When the touch keys are not

touched, the display card will enter the On/Off 1-key standby state, where the current reduces to

about 130nA@3V. When the On/Off main key is touched, the LCD will display “－－－－－－”,

in which condition Key 0~9, Key C and Key OK can be touched with the results being displayed

on the LCD. Touching the On/Off key again will turn off the LCD forcing it to enter the 1-key

standby state and awaiting a further wake-up. The function of the Key C is to delete the last key

code entered and shift left. The function of the Key OK is for confirmation with its current program

configuration displaying “－－－－－－”. This solution only is used to provide touch key

sensitivity tuning and as a PCB design reference. A picture of the physical product is shown in

Figure 2.

Figure 2

Operating Principles

For the Holtek touch key LCD display card solution, the BS67F2563 includes an ultra-low power

LXT oscillation circuit to provide calendar timing, 13 touch keys for PIN code and a challenge code

input. It also includes a 4×12 C-type LCD panel to display the operations. The standby current for

its 1-key standby wake-up and RTC timing can be less than 130nA@3V(Typ.). This solution

provides 13 touch key inputs, reducing the cost of traditional tactile switches and the labour cost of

bounding keys. The touch key sensitivity and scan times can be adjusted using firmware and the

solution can support up to 8 digit password display solutions. The main circuit is introduced below.



Hardware Description

Figure 3

The BS67F2563’s internal LXT oscillator needs to be matched with a 32768Hz crystal oscillator

with a specified CL≤7pF to achieve the optimum oscillation current. If the crystal oscillator CL is

larger, the oscillation current will increase. The oscillation frequency accuracy depends on the

crystal oscillator CL, external capacitance C3/C4 and the PCB parasitic capacitance. It is important

to pay special attention to the trace distances and sizes when laying out the PCB.

Figure 4

The provided LXT oscillator negative impedance reference requires at least 3 times the ESR

specification of the 32768Hz crystal oscillator as a safe value, to avoid oscillation problems during

mass production. These problems could be no oscillation or ceasing oscillation. This requires

special attention to be paid when choosing a particular 32768Hz crystal oscillator. The 32768Hz

crystal oscillator ESR of this solution is 65kΩ and the measured negative impedance of the

BS67F2563 is up to 500kΩ.



The LXT oscillation frequency is mainly related to the 32768Hz crystal oscillator CL specification.

For example, the external C3/C4 series equivalent capacitance value plus the PCB parasitic

capacitance equal to the crystal oscillator CL can provide an accurate 32768Hz oscillation frequency.

Developers can adjust the oscillation frequency to find a suitable C3/C4 capacitance value. It is

important to pay attention to the oscillation effect of C3/C4. Choosing C3/C4 values larger than CL

will result in a slower oscillation frequency, and vice versa. Figure 5 below shows the frequency

errors for different voltages and external C3/C4 capacitors.

Note: The influence of temperature on the frequency offset of the 32768Hz crystal oscillator is not

considered here.

It should be noted that oscilloscope probes should not be used to directly touch the XT1/XT2 pin

to view the oscillation frequency during measurement. Users can view the oscillation frequency

through I/O pin output.

Figure 5

The BS67F2563 includes an integrated C-type LCD driver, which supports different LCD power

supply modes set by the LCD control register depending on the voltage of the LCD liquid crystal.

If a 3V LCD screen is chosen, users can set the LVD (Low Voltage Detection) voltage to 2.7V and

turn on the internal voltage dividing mode. When the voltage is lower than 2.7V, the internal

reference voltage (1.04V) will be turned on to provide boosting to offer a stable contrast display.

Note that the VMAX pin should be connected to the MCU’s highest voltage level. The LCD circuit

is shown in Figure 6.



Figure 6

The BS67F2563 integrated capacitive touch key circuit uses PCB pads as the touch sense capacitive

inputs. Here an internal oscillation change is used to determine whether a touch action has occurred.

This solution allows a 1-key standby wake-up key to be specified, the scan times to be configured,

all keys to be scanned in the Auto Scan mode and also to tune the touch sensitivity.

Within the example program, the TKS_GLOBE_VARIES.INC is used to configure the touch keys,

the standby wake-up key and the touch sensitivity tuning.

Layout and Hardware Considerations

The external size of the display card is 85.60×53.98×0.8mm (ISO7816 standard) and the card

product has used a cold press process. Therefore, the length and width reserved for the PCB display

card should be reduced by 2mm. As the paper battery and LCD panel are components with a certain

height, the PCB should be hollowed out to reserve this height space. Also the allowed height for

related components should not exceed 0.3mm. The thickness of the PCB board including gold

immersion should not exceed 0.15mm.

Due to the limited size of the display card PCB, it is necessary to locate a suitable touch key pad.

This solution illustrates the case for placing 13 touch keys. It is recommended that the touch key

trace diameter is 6mil wide and the spacing is 5mil during layout. It is recommended during design

that only one key is scanned for each touch key module to avoid mutual key interference. Since the

thickness of the display card PCB board is 0.15mm, the front and back side grounding of the PCB

is important in order to avoid mutual key interference or interference from the back touches. Users

should refer to the PCB mesh ground design for this solution.

Developers should test the crystal oscillation frequency when designing the circuit. Select

appropriate C3 and C4 capacitors to match the oscillation frequency and take care to avoid any high

frequency circuits being placed nearby which could affect the oscillation characteristics. The

32768Hz crystal oscillator circuit should be as close as possible to the XT1 and XT2 pins and the

traces between the C3/C4 capacitors and the MCU VSS pin should be shortened.

Figure 7 and Figure 8 are the front and back PCB layout diagrams of the BS67F2563 touch key

LCD display card.



Figure 7

Figure 8

PCB BOM List

Table 1



Software Description

Start

MCU initialization

Turn off LCD and enter standby mode

Touch key scan

On/Off key touched ?

LCD displays “------”

Time Base On8s overflow？

Key C touched ? Key OK touched ? Key 0~9 touched ?

LCD last digit is deleted then shift to the left LCD displays “------”

LCD shifts to the right and displays the current

digit

Y

N

Y

Y Y Y

N

N N

Touch library initialization

USER_PROGARM

Figure 9

Initialization

After initial power on, the program will first initialize user application related data, including the

system clock, WDT, LVD, KEYOSC and touch key scan configuration. Special attention should be

paid to the I/O configuration to avoid any floating I/Os which will cause the static current to increase.

Main Program

The main program will first scan the touch keys to detect whether the On/Off key is touched or not. If

touched then the LCD will be turned on and will display “－－－－－－”. When any Key 0~9 is

touched, the LCD will display the first digit from the leftmost side. When the second key is touched,

the LCD display will shift to the right and display the current digit and so on. If Key C is touched, the

leftmost digit will be deleted and shifted left. If Key OK is touched, display “－－－－－－”.



After each touch key operation is finished, a time base counter is turned on to initiate an 8 second time

period. If there is no operation within 8 seconds, the LCD will be turned off and it will enter the ultra-

low power standby mode. In addition to the above operations, if it is already in the On state, touching

the On/Off key again will turn off the LCD forcing it to enter the ultra-low power standby mode.

Touch Software Package Description

To implement the touch key function, the Holtek touch software package should be used. This

software package is a complete HT-IDE3000 project, which has integrated a basic program structure

(MAIN_PROGRAM.asm) and reserves a user initialization program (USER_PROGRAM_INITIAL)

and a user main program (USER_PROGRAM). The software package will call the user initialization

program once during the power on initialization process and repeatedly call the user main program

during normal operation. For further use and modification of the software package, contact Holtek’s

and Bestsolution’s technical staff.

File Structure and Description

The software package contains two types of files:

1. ASM/.C application programs.

2. Files required for .INC/.H & .INI include. “.INI” is an underlying parameter file which is

recommended not to be modified.

The software package contains four parts, main program (MAIN_PROGRAM.asm), touch program

(BS67F2563_CTOUCH.INI), LCD driver (wizcard.c) and user program (USER_PROGRAM.c), as

shown in Figure 10.

MAIN_PROGRAM.asm MAIN_PROGRAM.inc TKS_GLOBE_VARIES.inc

BS67F2563_CTOUCH.INI

wizcard.c

USER_PROGRAM.c

include include

Figure 10

As the touch program adopts a library method, the corresponding program library

BS67F2563_CTOUCH_V600.OBJ needs to be loaded to implement the touch function. The

parameter settings of the related functions are setup in TKS_GLOBE_VARIES.inc.

BS67F2563_CTOUCH_V600.OBJ TKS_GLOBE_VARIES.incinclude

Figure 11



The library provides touch key related parameter settings whose details are as follows:

Parameter Name Function Value Range Recommended Value

SystemClock System frequency selection

0=4MHz 1=8MHz 2=12MHz

0

DebounceTimes Debounce times 0~15 2

AutoCalibrationPeriod Auto calibration period setting 0~15 4~8

HighSensitive High sensitivity setting 0=Off; 1=On 0 MaximumKeyHoldTime Maximum key hold time 0~15 1 (4 seconds) FastResponse Fast response setting 0=Off; 1=On 0

AutoFrequencyHopping Auto frequency hopping setting 0=Off; 1=On 1

OneKeyActive 1 key or all keys active 0=All keys active 1=One key active

1

PowerSave Low power setting 0=Off; 1=Low power 1 NoiseProtect Noise protection setting 0=Off; 1=On 1

MovingCalibration Dynamic calibration setting 0=Static; 1=Dynamic 1

MainFrequency KEYOSC frequency setting

0=1MHz 1=3MHz 2=7MHz 3=11MHz

1

HaltTouchScanRate Touch key scan rate setting

0=64ms 1=128ms 2=256ms 3=512ms

2

KeyNThreshold Trigger threshold 10~64 The smaller the value, the more sensitive.

Refer to the Operating Description chapter.

IO_TOUCH_ATTR Touch key selection 0=Off; 1=On Select according to actual application requirements.

WAKEUP_ATTR Wake-up key selection 0=Off; 1=On Select according to actual application requirements.

Table 2

Considerations for Use

1. The touch parameters listed in Table 2 can be adjusted in TKS_GLOBE_VARIES.INC.

2. The main parameters that affect the battery life of the product include SystemClock, PowerSave,

MainFrequency and HaltTouchScanRate, etc. Users should properly configure these parameters

according to their requirements.

3. Since the software package adopts a time-shared multi-work scheme, the touch response will be

delayed if the user program is executed for too long a time. It is recommended that the execution

time of the USER_PROGRAM does not exceed 10ms.

Used Resources

The used RAM and ROM sources are as follows. ROM Total Size : 16384 [4000h] Total Used : 2606 [0A2Eh] Total Remain : 13778 [35D2h] Total Percentage : 15% RAM Total Size : 2304 [0900h] Total Used : 247 [00F7h]



Operating Description

This solution provides functions for touch key sensitivity configuration, malfunction test,

measurement for 1-key wake-up standby current and scan current.

Touch Key Sensitivity Configuration and Malfunction Test The trigger threshold of each touch key can be configured in the program to adjust the touch

sensitivity.

1. If the thickness of the PCB board is 0.4mm, the recommended trigger threshold (KeynThreshold)

is “32”.

2. If the thickness of the PCB board is 0.15mm, the recommended trigger threshold (KeynThreshold)

is “16”.

In display card applications, due to factors such as the PCB board, a too high trigger threshold

configuration could cause poor sensitivity while a too low configuration will make the product too

sensitive and therefore easy to malfunction. Developers need to pay special attention to these areas

during debugging.

The PCB front and back sides adopt mesh grounding for isolation to avoid accidental touch or

interference. Users can use a key or other metal to test malfunctions.

Test Data

Current Measurement

In this solution, the system frequency is set to 4MHz and the touch key oscillator frequency is set to

3MHz. It has also distinguished between the 1-key standby wake-up current and the all touch key

scanned current. As the standby current of the ultra-low power series of MCU is extremely small, it is

recommended to use the KEYSIGHT 34461A 61/2 ammeter when conducting measurements to avoid

measurement errors. Refer to Table 3.

Test Item Test Condition VDD Specification Measured Value

ISTB In the standby mode, scan the touch key every 256ms 3V Typ. = 200nA

Max. = 250nA 127nA

IDD Under normal operation 3V N/A 695µA

Table 3

Note: The values are measured using the KEYSIGHT 34461A 61/2 ammeter.

Conclusion

This text has used the BS67F2563 MCU to introduce the Holtek touch key LCD display card

solution. The BS67F2563 provides an excellent ultra-low 1-key standby current of 127nA@3V,

allowing for a battery life as long as 3~5 years. The integrated touch keys and C-type LCD driver

circuits in the BS67F2563 further reduce the cost of the solution, making it very suitable for battery

applications such as display cards.



Reference Material

Reference file: BS67F2563 Datasheet.

For more information, refer to the Holtek official website: www.holtek.com.

Versions and Modification Information

Date Author Issue 2020.06.03 黃啓德 V1.00

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Touch Key LCD Display Card Reference Design...LCD displays “-----” LCD shifts to the right and...

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