dm00228871

UM1948
User manual
EVALSTPM3x-3PH evaluation board firmware
Introduction
The document describes the software implementation of the EVALSTPM3X-3PH power meter based on
the STM8S903K3 microcontroller and the STPM33 and the STPM34 metrology devices, with a firmware
within 8 kilobytes.
Besides 3-phase power meter can also be used as a reference for 1-phase power meter.
The evaluation board can be supposed as a whole “chip” (virtual 3-phase IC) application, to be
connected with an STM32 family microcontroller by SPI or UART.
Setting the STM8S903K3 microcontroller dummy, the STPM34 or the STPM33 can be controlled by the
external microcontroller independently via SPI interface. In this case, the firmware in the STM8S903K3
can be ported into external microcontroller such as an STM32 family device.
This manual includes the software structure introduction, the used microcontroller resources, the main
function interfaces and the program flowchart.
Regarding to the STM8S903K3, refer to datasheet "STM8S903K3 STM8S903F3" and RM0016
reference manual for more details.
December 2015
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www.st.com
Contents
UM1948
Contents
1
2
Overview .......................................................................................... 3
1.1
System architecture .......................................................................... 3
1.2
Used resources ................................................................................. 4
1.2.1
Hardware connections ........................................................................ 4
1.2.2
Software configuration ........................................................................ 5
1.2.3
MCU peripheral use............................................................................ 6
1.2.4
Firmware layer description ................................................................. 8
Main interfaces ................................................................................ 9
2.1
Interfaces of the STPM3x driver ........................................................ 9
2.1.1
void stpm3x_HwInit(TBool bUseSPI) ................................................ 9
2.1.2
TBool stpm3x_DataIO(TU16 nRdWtAddr,TU8*pTxDat,TBool
bUseCRC, TU8 *pRxDat) ................................................................................... 9
2.1.3
void stpm3x_IO_EnableLED(TBool bEnable) ................................. 10
2.1.4
TBool stpm3x_ReadReg32(TU8 nAddr, TU8 *pnVal) ...................... 10
2.1.5
TBool stpm3x_WriteReg32(TU8 nAddr, TU8 *pnVal) ...................... 10
2.1.6
TBool stpm3x_ReadTarReg32(TU8 nTarRow, TU8 *pnVal) ........... 10
2.1.7
TBool stpm3x_ReadRegBits(TU8 nAddr, TU8 nOffset, TU8
nBitNum, TU32 * pnVal) ................................................................................... 10
2.1.8
TBool stpm3x_WriteRegBits(TU8 nAddr, TU8 nOffset, TU8
nBitNum, TU32 nVal) ....................................................................................... 11
3
2.1.9
TBool stpm3x_RegRead(TU8 nReg, TU32 *pnVal) ......................... 11
2.1.10
TBool stpm3x_RegWrite(TU8 nReg, TU32 nVal) ............................ 11
2.2
Flowchart......................................................................................... 12
2.3
GUI communication command ........................................................ 12
Software design calibration .......................................................... 13
3.1
Pulse output generation .................................................................. 13
3.2
No-load condition judgement........................................................... 14
3.3
STM8 limitation ............................................................................... 14
4
Accuracy results ........................................................................... 15
5
Revision history ............................................................................ 17
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Overview
1
Overview
1.1
System architecture
The software is designed by following a platform independent approach. The driver and the
application layer can be ported to the other part number in the STM8, STM32 or even
Win32 platform.
The below figure shows the system architecture. It could be divided into 3 layers.
Figure 1: Project organization
Host Interface
(host_if.h, host_if.c)
Meas_app
(meas_app_3p.c,
meas_epulse_3p.c
meas_store_3p.c)
Driver / application program interface (API) layer
drv_stpm3x.c
drv_stpm3x_v3p.c
drv_stpm3x_reg_spi.c
Hardware abstraction layer (HAL)
STPM3x Drv HW access on STM8S (Drv_stpm3x_reg_ spi_stm8.c)
STM8 utilities
(ST_hal_util.c)
UART HW access (host_uart_stm8.c)
SPI HW access (host_spi_stm8.c)
General HW access
(st_ha l_ge n_stm8.c)
Configuration (st_app_hw_def_stm8.h)
Application layer code implementing 3-phase power meter functions
Platform independent code
HW accessing code STM8, STM32 or Win32
The entities below the hardware abstraction layer (HAL) belong to the hardware (HW)
access layer.
It implements the clock initialization, UART initialization, GPIOs initialization, HW
connection initialization between either the STPM34 or the STPM33 and the
microcontroller, software timer implementation, interrupt setting and so on.
The whole system can work on many target controllers such as the STM32, STM8 or even
Win32, if corresponding HW access layer is implemented. In the STM8 implementation, all
the HW information is defined in st_app_hw_def_stm8.h of each project directory. User
could simply modify this file and related source files to port software on different STM8 and
even STM32 microcontrollers.
The 2nd layer, hardware independent, is the driver layer/application program interface layer.
This layer supplies all interface functions between the STPM3x and the microcontroller
(STM8), and some special function routines, which implement the controlling operation to
the STPM3x. Above this layer, the application layer develops all functions by just calling
API layer functions, without need to focus on the STPM3x details and the bottom HW
implementation.
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Overview
UM1948
The application layer is the final goal of the entire application design. In this software, it
includes the energy pulse generation, energy data storing in EEPROM, energy related data
collecting and implementation of UART commands from the EVALSTPM3x-3PH GUI,
which is human-machine interface. Among the energy related data, energy values only are
read from the STPM3x registers (by API layer), power values are calculated by the STM8
(not by API layer). Further necessary and important information is obtained on GUI by
accessing the STPM3x registers (by API layer) via UART commands. At the same time,
calibration information is also transferred by GUI to microcontroller, then to STMP3x
registers (by API layer).
1.2
Used resources
1.2.1
Hardware connections
The block diagram of the entire application is shown below:
Figure 2: Application block diagram
HW UART
USB
O_M ISO
STPM34
ZCR 1, LED1, LED2
SCS1
RS485
I_M OSI, EN, SYN, SCL, 16M Hz
STM8
O_M ISO’
Energy pulses
ZCR 2, LED3, LED4
STPM33
SCS2
HW SP I
SPI
The below table describes the pin assignment of the STM8 on HW PCB V1.1.
Table 1: STM8S903K3 pin assignment
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Pin
Net name
Description
Remark
1
NRST
Reset pin
2
OSCIN
Resonator/ crystal in
3
OSCOUT
Resonator/ crystal out
4
VSS
GND
5
VCAP
1.8 V regulator capacitor
6
VDD
Digital power supply
21
PC4
I_CLK_MTR
8
PF4
O_Q_LED
9
PB7
O_P_LED
10
PB6
I_SCS1
Pin selection for the STPM34
29
PD4
I_SCS2
Pin selection for the STPM33
11
PB5
I_SYN
Supply 16 MHz to the STPM34 and the STPM33
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Overview
Pin
Net name
Description
Remark
13
PB3
I_EN
14
PB2
O_MISO
15
PB1
I_MOSI
16
PB0
I_SCL
25
PD0
O_MISO'
MISO is just for the STPM33
19
PC2
O_ZCR1
Timer1_channel2
20
PC3
O_ZCR2
Timer1_channel3
32
PD7
O_RTS_STM8
27
PD2
I_CTS_STM8
30
PD5
O_TX_STM8
31
PD6
I_RX_STM8
22
PC5
I_SCK_STM8
23
PC6
I_MOSI_STM8
24
PC7
O_MISO_STM8
18
PC1
O_LED1
7
PA3
O_LED2
17
PE5
O_LED3
28
PD3
O_LED4
12
PB4
O_INTCB
26
PD1
IO_SWIM
Software SPI, MISO is just for the STPM34
UART interface
Hardware SPI (PC5,PC6,PC7)
STPM34 LED pulse output
1.2.2
STPM33 LED pulse output
Software configuration
The latest HW PCB version is V1.1, for which “HW_STPM3X_3P_V2” macro must be
defined in file st_app_hw_def.h. To be flexible and save memory, many macro definitions
could be found in file stpm3x_app_config.h. Using IAR EWSTM8 1.41.1 compiler and the
below configuration, at least 7862 bytes Flash and at least 570 bytes RAM are required
under none optimization condition.
Table 2: Macro definition
Macro
Configuration
Remark
Off
Used as a convenient access (registers)
method, mask the detailed info of
registers. Refer to and to Section 2.1.10:
"TBool stpm3x_RegWrite(TU8 nReg,
TU32 nVal)"
STPM3x_CFG_USE_V3P_REG
Off
Used as a convenient access (registers)
method, in virtual 3-phase measurement
chip. The STPM34 and STPM33 are in a
unique virtual address, not split chips
STPM3x_CFG_USE_SW_EPULSE
On
Used to select different pulse output
implementation method. Refer to Section
3.1: "Pulse output generation"
STPM3x_CFG_USE_NAMED_REG
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Macro
Configuration
Remark
STPM3x_CFG_USE_HOST_UART
On
Used to select different interfaces to GUI.
In the software, UART is selected
STPM3x_CFG_USE_HOST_SPI
Off
Used to select different interfaces to GUI.
If on, select SPI interface
STPM3x_CFG_USE_PACK_INIT
On
Used to select different initialization
methods. If on, all registers are initialized
by 32-bit register writing method once; If
off, all registers are initialized by register
bit writing method one by one
STPM3x_CFG_CALC_ACT_POWER
On
Used for power (active, reactive)
calculations. It is always on
STPM3x_CFG_POLY_PHASE
On
Used to select different application
purposes. If on, 3-phase power meter is
available; if off, 1-phase power meter is
available
STPM3x_CFG_ENERGY_ACCU
On
Used for energy accumulation
calculations. It is always on
MCU peripheral use
All used peripherals on the STM8S903K3 are described in the below table.
Table 3: Application peripheral usage
Peripherals
TIMER 1
(16-bit)
TIMER 5
(16-bit)
Application
Interrupt function
Interrupt priority
STPM34 ZCR output of voltage
channel 1 or voltage channel 2
TIM1_CH2 input
capture interrupt
2
STPM33 ZCR output of voltage
channel
TIM1_CH3 input
capture interrupt
2
When
STPM3x_CFG_USE_SW_EPULS
E is configured as on, the timer
generates 64 ms time base to
update energy and power
Update interrupt
2
Update interrupt
3
(STPM3x_CFG_USE
_SW_EPULSE on);
2
(STPM3x_CFG_USE
_SW_EPULSE off)
0.25 ms time base:


TIMER 6
(8-bit)

6/18
Multiplied by 4 to get 1 ms
as system tick
When
STPM3x_CFG_USE_SW
_EPULSE is configured
as on, it accumulates
energy fragment by 0.25
ms time slot to decide if
the generated energy
pulses
When
STPM3x_CFG_USE_SW
_EPULSE is configured
as off, it detects 80 ms
time out for pulse width
control
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Overview
Peripherals
Application
Interrupt function
Interrupt priority
PC1 rising edge to indicate P
pulse from the STPM34 (used
when
STPM3x_CFG_USE_SW_EPULS
E is configured as off)
EXTI
3
PA3 rising edge to indicate Q
pulse from the STPM34 (used
when
STPM3x_CFG_USE_SW_EPULS
E is configured as off)
EXTI
3
PE5 rising edge to indicate P
pulse from the STPM33 (used
when
STPM3x_CFG_USE_SW_EPULS
E is configured as off)
EXTI
3
PD3 rising edge is to indicate Q
pulse from the STPM33 (used
when
STPM3x_CFG_USE_SW_EPULS
E is configured as off)
EXTI
3
PB4 falling edge to indicate the
STPM3x event (the STM8S
should read related registers to
inquire which event in which chip)
EXTI
2
UART
UART interface to GUI
UART Rx interrupt
1 (the lowest priority)
SPI
SPI interface to GUI
SPI Rx and Tx interrupt
1 (the lowest priority)
EEPROM
Stores energy data to EEPROM
inside the STM8
No
EXTI


GPIO


GPIO simulation of SPI to
communicate with the
STPM3x
CCO to provide 16 MHz
to the STPM3x
GPIO level polling to
detect CTS from GUI
GPIO level control to
generate P and Q energy
pulses respectively
No
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1.2.4
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Firmware layer description
The below table lists the main files of different firmware layers.
Table 4: Main files
Layer
File name
Hardware
abstraction
layer
Driver
layer
Application
layer
Interrupt
.h files
Brief
Host_spi_stm8.c
STM8 SPI based communication with GUI
Host_uart_stm8.c
STM8 UART based communication with GUI
St_hal_gen_stm8.c
HAL implementation on the STM8
Drv_stpm3x_reg_spi_stm8.c
STPM3x SPI initialization for the STM8
St_hal_util.c
Utility function implementation to software timer and
other utilities
Drv_stpm3x.c
Definition of the STPM3x driver
Drv_stpm3x_reg_spi.c
STPM3x register SPI access implementation
Drv_stpm3x_v3p.c
Virtual 3-ph metering IC based on the STPM3x
Host_if.c
HOST communication demo with private protocol
Meas_app_3p.c
3-ph meter measurement based on the STPM3x
Meas_epulse_3p.c
3-ph energy pulse generation operations based on the
STPM3x
Meas_store_3p.c
3-ph meter storage definition for the STPM3x base
meter
Stm8s_it.c
Main interrupt service routines
Stpm3x_app_config.h
Configuration file of the STPM3x application
St_app_hw_def.h
Hardware definition on the STM8
Drv_stpm3x.h
Definition of the STPM3x driver
Drv_stpm3x_reg.h
Definition of the STPM3x register operations
Drv_stpm3x_v3p.h
Virtual 3-ph metering IC based on the STPM3x
Stpm3x_app_config.h is the basic system function configuration file. Different
options may change the software implementation methods, or select different
applications, or mask some unimportant functions to save memory according to
applications. Please refer to Table 2: "Macro definition" for detailed description.
St_app_hw_def.h is the hardware definition file related to connection. It is
necessary to change it accordingly if some pin connection has changed (and
possibly, it is also necessary to change some routines in Stm8s_it.c).
Drv_stpm3x.h is the STPM3x driver prototype definition file. In the file, all interface
functions between the STPM3x and MCU are declared. Drv_stpm3x_v3p.h is the
driver prototype definition file (based on Drv_stpm3x.h) when all the STPM3x
chips are looked as a whole, that is, a virtual 3-ph metering chip.
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Main interfaces
2
Main interfaces
2.1
Interfaces of the STPM3x driver
The interface to application layer is mainly driver layer since it involves the communication
between the STPM3x and microcontroller. It can also be used by other applications based
on different platforms. Besides, some initialization functions related to platform are also
introduced here because of their importance.
2.1.1
void stpm3x_HwInit(TBool bUseSPI)
Description: hardware initialization of pins connected to the STPM3x and setting of the
STPM3x communication interface.
Parameters:

bUseSPI

True, sets SPI interface

False, sets UART interface
Return value: none.
Remarks: the timing sequence is strict, so control if different system clocks or platforms
are used.
2.1.2
TBool stpm3x_DataIO(TU16 nRdWtAddr,TU8*pTxDat,TBool bUseCRC,
TU8 *pRxDat)
Description: GPIO simulation of SPI communication (4-line) with the STPM3x. If CRC is
used, 5-byte frame is sent and 5-byte frame is received.
Parameters:




nRdWrAddr: register address for read or write

High byte stores write address

Low byte stores read address

When read, it sets high byte to 0xFF

When write, it sets low byte to 0xFF
*pTxDat: stores the 5-byte frame to be sent
*pRxDat: stores the 5-byte frame to be received
bUseCRC

True, the frame is 5 bytes

False, the frame is 4 bytes
Return value: true, CRC of received frame is right; false, CRC of received frame is wrong.
Remarks: SCL simulation should be 50% duty.
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void stpm3x_IO_EnableLED(TBool bEnable)
Description: Enable EXTI for LED pins. EXTI can only be enabled after the STPM3x
register initialization.
Parameters:

bEnable

True, enable EXTI

False, disable EXTI
Return value: none.
2.1.4
TBool stpm3x_ReadReg32(TU8 nAddr, TU8 *pnVal)
Description: Read 32-bit data of some registers.
Parameters:


nAdd: register address (even number), listed in the register map of datasheet
*pnVal: 32-bit data read from the register
Return value: true, success; false, fail.
2.1.5
TBool stpm3x_WriteReg32(TU8 nAddr, TU8 *pnVal)
Description: write 32-bit data to some registers.
Parameters:


nAddr: register address (even number), listed in register map of datasheet
*pnVal: 32-bit data to be written to the register
Return value: true, success; false, fail.
2.1.6
TBool stpm3x_ReadTarReg32(TU8 nTarRow, TU8 *pnVal)
Description: read 32-bit data of some registers from the STPM34 or STPM33.
Parameters:


nTarRow: MSB indicates which chip to choose, other bits are register’s row address,
listed in the register map of datasheet
*pnVal: 32-bit data read from the register
Return value: true, success; false, fail.
2.1.7
TBool stpm3x_ReadRegBits(TU8 nAddr, TU8 nOffset, TU8 nBitNum,
TU32 * pnVal)
Description: some continuous bits of the register 32-bit data are read.
Parameters:




nAddr: register address (even number), listed in the register map of datasheet
nOffset: offset of the 32-bit data, the value can be 0 to 31
nBitNum: bit number beginning from the offset of 32-bit data, the value can be 1 to 32
*pnVal: data read from the register with the offset and bit number setting
Return value: true-success; false-fail.
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2.1.8
Main interfaces
TBool stpm3x_WriteRegBits(TU8 nAddr, TU8 nOffset, TU8 nBitNum,
TU32 nVal)
Description: some continuous bits are written to the register position beginning from
offset.
Parameters:




nAddr: register address (even number), listed in register map of datasheet
nOffset: offset of the 32-bit data, the value can be 0 to 31
nBitNum: bit number beginning from the offset of 32-bit data, the value can be 1 to 32
nVal: data to be written to the register with the offset and bit number setting
Return value: true-success; false-fail.
2.1.9
TBool stpm3x_RegRead(TU8 nReg, TU32 *pnVal)
Description: some continuous bits of the register predefined by the array and index are
read. The detailed information (register address, offset and bit number) is encapsulated
inside the array.
Parameters:


nReg: element index of the predefined array. The value is related to some enum
definition, showing the register meaning
*pnVal: data readout
Return value: true-success; false-fail.
2.1.10
TBool stpm3x_RegWrite(TU8 nReg, TU32 nVal)
Description: some continuous bits are written to the register predefined by the array and
index. The detailed information (register address, offset and bit number) is encapsulated
inside the array.
Parameters:


nReg: element index of the predefined array. The value is related to some enum
definition, showing the register meaning
nVal: data to be written
Return value: true-success; false-fail.
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Flowchart
Figure 3: Application flowchart
2.3
GUI communication command
GUI command frame format:
TX: { STX | Target(4b):Func(4b) | Addr | Val[2] (LSBF) | Addr2 | 00 | CS8 }
RX: { STX | Target(4b):Func(4b) | ErrCode | Val[4] (LSBF) | CS8 }
STX: 0x68
Target: 01/02/03/08, to the STPM34/STPM33/both/virtual 3-PH, @refer ESTPM3xTar
Func: 00/01/02/03/04, /Reset/Latch/Direct IO/Read/Write, @refer ESTPM3xFunc
Addr: 255 x 4B STPM3x RAM/virtual 3-PH RAM (needs to be even number to read)
Val[2]: the value to be written, LSBF
Addr2: only available in direct IO mode, when Addr is ReadAddr and Addr2 is WriteAddr
Val[4]: the value read, LSBF
CS8: 8-bit check sum of the frame
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Software design calibration
3
Software design calibration
3.1
Pulse output generation
Pulse output generation is a key point of the application, since accuracy tests are carried
out using the pulses/kWh produced by the power meter.
There are two methods to generate the energy pulses.

Software pulse method (STPM3x_CFG_USE_SW_EPULSE is configured as on)
The pulse is generated by adding up the energy (DeltaE) every time slot (0.25 ms) when
the current time slot elapses one by one. Once the accumulated energy exceeds the
threshold, which represents the energy of just one pulse, MCU outputs 80 ms-width pulse
to light P LED or Q LED. Obviously, the shorter time slot, the more accurate the
measurement results. However, a tradeoff between the time slot and MCU efficiency is
necessary, since too short time slot leads to a heavy MCU workload.

Hardware pulse method (STPM3x_CFG_USE_SW_EPULSE is configured as off)
The pulse is generated by external interrupts from 4 LED pins of the STPM34 and
STPM33.
In the interrupt service routine, when the number of active energy LED pulses exceeds the
threshold, MCU outputs 80 ms-width pulse to P LED (and the same for reactive energy to
Q LED).
The number of pulses/kWh from all LED pin STPM3x chips is the threshold for the 3-ph
power meter to output just one active energy pulse on LED P. This threshold depends on
the application design and particularly from analog font end component choice.
Microcontroller continuously counts interrupt occurrences to light P or Q LED at proper
time.
Note:
1.
2.
3.
4.
5.
The threshold is clearly different in two methods. In software pulse method, it indicates
a fixed energy value. In hardware pulse method, it indicates a fixed number derived
from pulse constant (imp/kwh). However, the threshold is both determined by
hardware parameters (R1, R2, kS ) and software configuration (LEDPWM in DSP_CR1
and DSP_CR2), just different in unit (ws or impulse number).
To obtain better accuracy, the operation of ending P and Q pulse after 80 ms is also in
0.25 ms interrupt service routine, since both of edges need to be accurate.
As explained in the application peripheral usage table, the used MCU resources are
different between the two methods. In the hardware pulse method, the pulse output
depends on 4-pin interrupt number, so 4 EXTI are necessary. However, in the
software method, the energy is calculated by adding up the “energy fragment” after
each time slot, so the 4-pin interrupt is not needed. But a proper time slot (0.25 ms) is
necessary; moreover, the “energy fragment” must be updated in a short interval if the
current power changes fast. It is 64 ms (2^6) generated from hardware timer so that
the interrupt and processing timing is in good condition and the power of two is
convenient for multiplication and division on the STM8 platform. It is less than the
shortest interval (about 124 ms) at maximum power load (3*100A, 110%Un).
Only 0.25 ms and 64 ms timings are coming from MCU timer directly, while all other
timers (second, minute, hour, day, week, month and year) are software timers, derived
indirectly from 0.25 ms.
In the above 2 methods, the accuracy influence factors are different:
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Software design calibration


3.2
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In the hardware pulse method, setting the highest EXTI priority, and the interval
time (longer or shorter) of energy register reading is an important factor for the
accuracy of energy displayed on GUI.
In software pulse method, the fixed time slot interrupt and the time interval
accuracy of energy register reading (update energy fragment) have the highest
impact on accuracy.
No-load condition judgement
When STPM3x_CFG_CALC_ACT_POWER is configured as on, if active power is less than
2.2 W ( PowerThreshold*Plsb) on A, B, C single phase or 3-ph totally, a no-load flag is set
to 1.
When STPM3x_CFG_CALC_ACT_POWER is configured as off, no-load condition is
determined through apparent power, Vrms*Irms (please note Vlsb*Ilsb=Plsb>>2.2 W).
3.3
STM8 limitation
Some application attention points are reported below:
1.
2.
3.
4.
14/18
The STM8 is MSBF, but the STPM3x is LSBF, by default, this has to be taken into
account in data conversion between the STM8 and the STPM3x.
Considering that the STM8 is 8-bit microcontroller, single byte variable is proper in
most cases.
The STM8 computation performance is poor, especially the float number multiplication
and division. Only the power calculation is finished by STM8, which is well done by left
and right shift according to proper time slot (2N). Other calculations, for example,
frequencies, phase angle, power factor are calculated on GUI.
In hardware pulse method, O_LED1, O_LED2, O_LED3 and O_LED4 are located in
different ports (port A, port C, port D, port E respectively). This is necessary because
pins of the same port share the same interrupt by logical OR, so in some cases it is
impossible to distinguish them correctly, if they are very close to each other.
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Accuracy results
Accuracy results
With the above firmware implementation and after the device calibration, the following
accuracy curves, for active power, have been taken on P LEDs.
Testing conditions are:
VN = 230 V
IN = 5 A
fline = 50 Hz
CP = 400 pulses/kWh
In figures below, accuracy results are benchmarked with IEC 62053-22 normative
requirement for class 0.2 meters.
Table 5: Active power error overcurrent
Applied current
[A]
Full scale percentage
[%]
10
Percentage error [%]
cosphi = 1
cosphi = 0.5
ind
cosphi = 0.5
cap
200
0,067
0,046
0,124
5
100
0,068
0,028
0,128
2.5
50
0,078
0,016
0,088
1
20
0,066
0,038
0,060
0.5
10
0,091
-0,300
-0,250
0.25
5
0,065
0,046
0,124
0.1
2
-0,097
0.028
0,128
0.05
1
-0,271
Figure 4: Active power accuracy at cosphi = 1
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Figure 5: Active power accuracy at cosphi = 0.5 inductive and capacitive
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Revision history
Revision history
Table 6: Document revision history
Date
Revision
09-Dec-2015
1
Changes
Initial version.
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