Holtek HT16C22 Instructions for use

Electric Meter Applications Using the HT16C22

D/N：AN0255E

Introduction

The HT16C22 provides a maximum display driver pin of 4 Commons and 44 Segments

and is driven by I2C communication control. The following application content describes

the related setup and application methods for a 4x40 LCD electric meter driven by the

HT16C22.

Operation Principles

The HT16C22 device is a memory mapping and multi-function LCD controller driver. With

its software configuration functions, it is very suitable for various LCD applications.

HT16C22 Features:

Operation Voltage：2.4V～5.5V

Internal 32kHz RC oscillator

Bias : 1/2 or 1/3

Duty : 1/4

I2C-bus interface

Two selectable LCD frame frequencies: 80Hz or 160Hz

44×4 bits RAM for display data storage

4 kinds of flashing modes

Read/write address auto increment

Internal 16-level voltage adjustment to adjust LCD operating voltage

Low power consumption

VLCD pin for adjustable LCD operating voltage

Electric Meter Applications Using the HT16C22

HT16C22 Related Command Setup

HT16C22 Operating Mode

The operating mode of the HT16C22 can be setup using Mode Set. The settings are as

follows.

Bit 15 14 13 12 11 10 9 8

--- 1 0 0 F S E 0 M0

M0 : LCD driver offset voltage mode bit

0 : 1/3 Bias；1 : 1/2 Bias

S, E : LCD display status mode bit

0x : Disable the internal system oscillator, LCD display and LCD bias generator

10 : Enable the internal system oscillator and disable the LCD display and LCD bias

generator

11 : Enable the internal system oscillator and disable the LCD display and LCD bias

generator

F : LCD frame frequency select bit

0 : fLCD = 80Hz；1 : fLCD=160Hz

HT16C22 Address Pointer

The HT16C22 contains 22 display RAM addresses which can be set through the address

pointer for the corresponding RAM value.

Bit 15 14 13 12 11 10 9 8

--- 0 0 0 A4 A3 A2 A1 A0

A4~A0 : RAM address. The maximum A4~A0 value should not be more than 22.

HT16C22 Blinking Setting Command

Bit 15 14 13 12 11 10 9 8

--- 1 1 0 0 0 0 B1 B0

B1, B0 : LCD blinking frequency control bit.

00 : blinking switch

01 : 2Hz

10 : 1Hz

11 : 0.5Hz

HT16C22 VLCD Voltage Adjustment

Bit 15 14 13 12 11 10 9 8

--- 0 1 DE VE DA3 DA2 DA1 DA0

DE : VLCD and SEG select pin

0 : VLCD pin

1 : SEG pin

VE : Internal bias voltage adjustment bit

0 : Disable the internal voltage adjustment

1 : Enable the internal voltage adjustment

DA3~DA0 : Adjust the VLCD output voltage as shown in the table below:

Electric Meter Applications Using the HT16C22

Note: When the DE and VE bits are in the following status, note the DA3~DA0 bit

setup.

DE VE Special Notes

0 0

When VLCD connects to VDD through a resistor, the DA3~DA0 bits must

be set to 0000.

When VLCD directly connects to VDD, the DA3~DA0 bits must not be

set to 0000.

0 1

The external MCU can detect the VLCD voltage.

1 0

The bias voltage is provided by VDD in the HT16C22.

When the internal voltage-follower (OP3) is disabled, it is not

necessary to setup DA3~DA0.

1 1 ------

HT16C22 Operation Flow

HT16C22 Initialization

When using the HT16C22, start with an initialization using the following steps:

Step 1: Enable the HT16C22 internal system clock

Step 2: Set the HT16C22 Internal LCD bias voltage

Step 3: Set the HT16C22 LCD frame frequency

Step 4: Set the HT16C22 VLCD and Seg reset pins

Step 5: Set the HT16C22 LCD blinking frequency

HT16C22 Data Read/Write

The HT16C22 data read/write setting steps are:

Step 1 : Set the corresponding address

Step 2 : Write operation to the display data RAM

Step 3 : Data display

HT16C22 Communication Method

The HT16C22 communicates with external devices using its I2C interface.

Start and end I2C communication signal

The I2C communication Start signal (figure 1) and Stop signal (figure 2) are shown

below:

Electric Meter Applications Using the HT16C22

Figure 1 Start Signal

Figure 2 Stop Signal

I2C communication data operation

When SCL is high, the SDA data is valid. When SCL is low, the SDA data changes as

shown in figure 3.

Figure 3 Data Operation

Byte transmission in the I2C communication

There must be an acknowledge signal within every 8 bits of data transmitted by the I2C.

When the acknowledge signal is zero, transmission will continue. When the signal is 1,

transmission stops. After the acknowledge signal “0” is received, the master device can

send a Stop signal to force the data transmission to end as figure 4 below shows.

Figure 4 Byte Transmission

Electric Meter Applications Using the HT16C22

I2C Communication Write Operation

A byte write operation requires a Start signal, a read/write flag (0: write, 1: read), one

valid slave address, data and a stop signal. After each step, the device responds with

an ACK as shown in figure 5.

Figure 5 Byte Write Operation

Page Write Operation: successive data write operation. The address pointer will be

incremented by 1 automatically for a write operation to the next address. When the

internal address pointer reaches the maximum memory address, which is 21H, the

address pointer will be reset to 00H as shown in figure 6 below.

Figure 6 Page Write Operation

I2C Read Operation

The read operation is shown in figure 7 below. The address pointer will be incremented

by 1 for a read operation to the next address. When the internal address pointer

reaches the maximum memory address, which is 21H, the pointer will be reset to 00H.

The consecutive address reading cycle will continue until the master sends a Stop

signal.

Figure 7 Read Operation

Electric Meter Applications Using the HT16C22

HT16C22 Electric Meter Application

Figure 8 Electric Meter LCD

Figure 8 illustrates an electric meter interface, which shows indications such as the

amount, voltage, current, consumption and remote copy etc.

Application Circuit

HT16C22

VDD

SDA

SCL

VSS

COM0

COM1

COM2

COM3

SEG0

SEG1

SEG2

SEG3

SEG4

SEG5

SEG6

SEG7

SEG8

SEG9

SEG10

SEG11

SEG12

SEG13

SEG14 23

SEG14 24

SEG16 25

SEG17 26

SEG18 27

SEG19 28

SEG20 29

SEG21 30

SEG22 31

SEG23 32

SEG24 33

SEG25 34

SEG26 35

SEG27 36

SEG28 37

SEG29 38

SEG30 39

SEG31 40

SEG32 41

SEG33 42

SEG34 43

SEG35/VLCD 44

IC2

HT68F30

PA0/C0X/TP0_0

VSS

PB4/XT2

PB3/XT1

PB2/OSC2

PB1/OSC1

VDD

PB0/RES

8PB5/RSCS 9

PA7/SCK/SCL 10

PA6/SDI/SDA 11

PA5/C1X/SDO 12

PA4/INT1/TCK1 13

PA3/INT0/C0- 14

PA2/TCK0/C0+ 15

PA1/TP1A 16

IC1

VDD

SDA

SCL

GND

COM0

COM1

COM2

COM3

SEG0

SEG1

SEG2

SEG3

SEG4

SEG5

SEG6

SEG7

SEG8

SEG9

SEG10

SEG11

SEG12

SEG13

SEG14

SEG15

SEG16

SEG17

SEG18

SEG19

SEG20

SEG21

SEG22

SEG23

SEG24

SEG25

SEG26

SEG27

SEG28

SEG29

SEG30

SEG31

SEG32

SDA

SCL

GND

VDD

1kR2

COM0

COM1

COM2

COM3

SEG0

SEG1

SEG2

SEG3

SEG4

SEG5

SEG6

SEG7

SEG8

SEG9

SEG10

SEG11

SEG12

SEG13

18 SEG14 19

SEG15 20

SEG16 21

SEG17 22

SEG18 23

SEG19 24

SEG20 25

SEG21 26

SEG22 27

SEG23 28

SEG24 29

SEG25 30

SEG26 31

SEG27 32

SEG28 33

SEG29 34

SEG30 35

SEG31 36

LCD1

COM0

COM1

COM2

COM3

SEG0

SEG1

SEG2

SEG3

SEG4

SEG5

SEG6

SEG7

SEG8

SEG9

SEG10

SEG11

SEG12

SEG13 SEG14

SEG15

SEG16

SEG17

SEG18

SEG19

SEG20

SEG21

SEG22

SEG23

SEG24

SEG25

SEG26

SEG27

SEG28

SEG29

SEG30

SEG31

100k

104

VDD

RES

Description: The figure above is an electric meter LCD diagram. The hardware

connection is as follows. Set PA7 to SCL, PA6 to SDA and PA0 as the key.

Electric Meter Applications Using the HT16C22

Special Notes:

During PCB Layout, the bypass capacitor C1 and C2 should be as close as possible to

the related IC and must have their external VDD and GND lines connected to the

bypass capacitors before connecting to the corresponding VDD and VSS pins of the

IC.

When the VLCD/SEG35 in the HT16C22 is set as a SEG pin and not in use, it can only

be placed into a floating condition as it is not able to connect to VDD through a resistor.

S/W Flowchart

Electric Meter Applications Using the HT16C22

Program Description

Initialize the main program including the RAM, I/O and SFR. The I2C initialization is the

same as the initialization of the HT16C22, such as to the HT16C22 internal system clock

control, LCD bias voltage selection, frame frequency selection, VLCD/SEG pin selection

and the LCD blinking frequency selection. The display program main purpose is to show

the related conditions. The display of this program contains eleven parts which can be

switched using key control. The display results are as follows:

1st screen: displays the whole LCD content

2nd screen: displays the voltage with a result of 220.0V

3rd screen: displays the current with a result of 5.160A

4th screen: displays the power consumption with a result of 3.240kW

5th screen: displays the power-on duration with a result of 82760.5h

6th screen: displays the overall power consumption with a result of 4651.25kWh.

7th screen: displayss the power factor with a result of COSØ 1.000

8th screen: displays the meter number with a number of 12345678

9th screen: displays the unit price with a value of 0.45 NT dollars

10th screen: displays the overall consumption amount with an amount of 98637.45 NT

dollars

11th screen: displays the surplus amount with a value of 0.85 NT dollars and a message

reminding the user to purchase more electricity

Conclusion

The above content has introduced a way to drive an LCD electric meter using the

HT16C22.

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