Holtek HT16C22 Instructions for use
Electric Meter Applications Using the HT16C22
1
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
2
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
3
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
4
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
5
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
6
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
1
SDA
2
SCL
3
VSS
4
COM0
5
COM1
6
COM2
7
COM3
8
SEG0
9
SEG1
10
SEG2
11
SEG3
12
SEG4
13
SEG5
14
SEG6
15
SEG7
16
SEG8
17
SEG9
18
SEG10
19
SEG11
20
SEG12
21
SEG13
22
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
1
VSS
2
PB4/XT2
3
PB3/XT1
4
PB2/OSC2
5
PB1/OSC1
6
VDD
7
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
S1
1kR2
COM0
1
COM1
2
COM2
3
COM3
4
SEG0
5
SEG1
6
SEG2
7
SEG3
8
SEG4
9
SEG5
10
SEG6
11
SEG7
12
SEG8
13
SEG9
14
SEG10
15
SEG11
16
SEG12
17
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
R1
104
C1
104
C2
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
7
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
8
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.
Table of contents
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