June 2006 Rev 1 1/29 AN2283 Application note uPSD3400 PWM API with R/C Servo Motor Control Example (PCM) Introduction The μPSD3400 combines a high-performance 8051-based microcontroller with peripherals to facilitate the design of complex applications. One such peripheral is the PCA (Programmable Counter Array). There are two PCAs in the uPSD3400 that operate independently of each other and in various modes that include capture, timer, toggle output, and PWM (8-, 10-, or 16-bit PWM mode with a fixed frequency or 8-bit mode with a variable frequency). Each PCA has three TCM (Timer Counter Modules) that can provide up to six PWM outputs. PWM is used in many applications that include LED brightness control, servo motor control, and AC/ DC motor speed control. This application note describes how to use the μPSD3400 Programmable Counter Array (PCA) logic in Pulse Width Modulation (PWM) mode for Radio Control (R/C) servo motor control. We provide an introductory background for understanding servo motor control and PWM, and show how PWM is easily implemented using the μPSD 3400. Note that all future references to servo motors in this document are of Radio Control (R/C) type. Servo motors are widely used in motion control applications that require a motor drive to position a mechanical device. One common way to control the servo motor is by using PWM, where the duration of the PWM pulse encodes the angular position of the servo motor shaft. The PCA subsystem in the uPSD3400 provides 11-bits of pulse encoded resolution (measured). Additionally, we describe an Application Programming Interface (API) that provides a high- level interface to the PCA subsystem. API routines are provided specifically for servo motor control, considering typical servo motor design. We demonstrate that the μPSD3400 PCA hardware and the PWM API offer a wide range of flexibility and ease-of-use for PWM programming. www.st.com
Transcript
June 2006 Rev 1 1/29
AN2283Application noteuPSD3400 PWM API
with R/C Servo Motor Control Example (PCM)
IntroductionThe µPSD3400 combines a high-performance 8051-based microcontroller with peripherals to facilitate the design of complex applications.
One such peripheral is the PCA (Programmable Counter Array). There are two PCAs in the uPSD3400 that operate independently of each other and in various modes that include capture, timer, toggle output, and PWM (8-, 10-, or 16-bit PWM mode with a fixed frequency or 8-bit mode with a variable frequency). Each PCA has three TCM (Timer Counter Modules) that can provide up to six PWM outputs. PWM is used in many applications that include LED brightness control, servo motor control, and AC/ DC motor speed control.
This application note describes how to use the µPSD3400 Programmable Counter Array (PCA) logic in Pulse Width Modulation (PWM) mode for Radio Control (R/C) servo motor control. We provide an introductory background for understanding servo motor control and PWM, and show how PWM is easily implemented using the µPSD 3400. Note that all future references to servo motors in this document are of Radio Control (R/C) type.
Servo motors are widely used in motion control applications that require a motor drive to position a mechanical device. One common way to control the servo motor is by using PWM, where the duration of the PWM pulse encodes the angular position of the servo motor shaft. The PCA subsystem in the uPSD3400 provides 11-bits of pulse encoded resolution (measured).
Additionally, we describe an Application Programming Interface (API) that provides a high-level interface to the PCA subsystem. API routines are provided specifically for servo motor control, considering typical servo motor design.
We demonstrate that the µPSD3400 PCA hardware and the PWM API offer a wide range of flexibility and ease-of-use for PWM programming.
PWM is a digital mechanism for representing an analog scale, and is used in control (PWM out) and measurement (PWM in) applications. In this application note, we illustrate a control application using the µPSD3400, although, the same hardware can also be used for measuring analog signals.
We first give an introduction to servo motor control, a positioning application, followed by a tutorial on PWM and its application to servo motor control.
1.1 Servo motor control (PWM for digital output applications)A servo motor has an output shaft that can be positioned by an encoded control signal. The motor drives the angular position of the controlled device.
Servo motors have three wires:
● +5V
● GND
● control
The control signal is used to control the angular position of the output shaft. This signal is encoded using PWM. The pulse duration determines the position of the shaft and as long as the code is present on the signal, the shaft position is maintained.
The motor rotates the shaft in the shortest direction to the position indicated by the encoded signal then stops shaft rotation. Servo motor control signals typically have a 20 msec period. The duty cycle (Pulse width modulation (PWM for analog output applications)) of the pulse within the period encodes the shaft position:
● -45° rotation is achieved with a 1 msec pulse; a duty cycle of 5%
● 0° rotation (the neutral position) is achieved with a 1.5 msec pulse; a duty cycle of 7.5%
● +45° rotation is achieved with a 2 msec pulse; a duty cycle of 10%
This is also known as PCM (Pulse Coded Modulation). With servo motor control, the width of the pulse is a code representing a desired shaft position.
1.2 Pulse width modulation (PWM for analog output applications)PWM is a modulation technique whereby the width of a pulse over the period of a signal, known as the duty cycle, is varied to represent the amplitude of an analog signal. Digital logic that implements PWM can vary the pulse width to achieve various amplitudes, varying the period to suit the application hardware requirements.
PWM approximates an analog signal by averaging voltage over time. Averaging the duty cycle over time is equivalent to an average analog voltage. The duty cycle is the percentage of time the signal is high for the given period. Figure 1 shows the relationship of duty cycle to period for a PWM signal.
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Figure 1. PWM signal
Duty Cycle is expressed as the percentage of time the signal is high for the given period.
duty cycle = 100 x (tdutycycle) / (tperiod)
For example, a 10% duty cycle applied to a 5Vcc signal approximates an analog voltage of 0.5V once this signal is averaged by an integrator/filter circuit.
GND
VCC
tdutycycletperiod
Description of PWM using the PCA AN2283
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2 Description of PWM using the PCA
This section shows how PWM is implemented using the µPSD3400 PCA.
2.1 PCA architecture for PWMPWM is one of four PCA modes and can be configured for 8-, 10-, or 16-bit fixed frequency resolution, or for 8-bit programmable frequency. A number of clock input sources are also available, depending on application requirements.
Programmable PCA registers are used to configure the operation of the PCA, to monitor status and to handle PCA events, such as interrupts on timer overflow. Figure 2 shows the PCA logic and programmable registers. The µPSD3400 has two PCA blocks, PCA0 and PCA1. Each PCA block controls three output signals. This allow the designer to simultaneously control or monitor six independent channels.
Figure 2. PCA0 block diagram
The uPSD34xx has two PCAs called PCA0 and PCA1. The block diagram for PCA0 is shown in Figure 2 and the different parts are discussed in the following paragraphs. Note that since PCA0 and PCA1 function in the same way, the description for PCA0 also applies to PCA1.
2.1.1 PCA clock source
There are three sources of clock input available for the PCA, two internal clock sources and one external. In this application note, we use PCA0CLK to drive the PCA. PCA0CLK is derived from the CPU clock with a 4-bit selectable divider that includes division rates of 1, 2, 4, 8 on up to 32768 by powers of 2. The other available internal clock source is the Timer 0 overflow. The external clock source is available through port pin P4.3/ECI (External Clock Input). CLKSEL0/1 are used to select the clock source.
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2.1.2 Clock source control
There are three control bits that determine whether the clock source is passed on to the 16-bit up timer/counter. EN_ALL (Enable All) is a signal that simultaneously turns on the clock source to PCA0 and PCA1. It is especially useful, for example, when you need 4 to 6 PWM outputs that must have synchronized periods.
EN_PCA is used to individually enable the clock source to the PCA and PCAIDLE determines whether or not the clock source is provided to the PCA when the MCU is in the idle mode.
2.1.3 Timer/counter, overflow, and interrupt
In the 16-bit PWM mode, PCACH0 and PCACL0 are used as the high and low bytes of the 16-bit timer. When the timer overflows, the OVF0 bit is set and the timer continues counting. If this interrupt is enabled (EOVFI), the PCA interrupt is generated. In this application note we don't use the PCA interrupt.
2.1.4 Timer/counter modules and output pins
There are three Timer/Counter Modules (TCM) per PCA. Each TCM is 16 bits wide and has an optional output available on a port 4 pin (CEX0, CEX1, or CEX2). The port 4 pins are multifunctional and the function of each pin is selected using the port 4 special function registers (P4SFS0 and P4SFS1).
When the count in the timer matches the value in the TCM register, the output is switched from low to a high. When the 16-bit timer overflows, the output switches from high to low. So, the value written to the TCM register determines the pulse width for the respective PWM output (CEXn).
Figure 3 shows the registers that implement the PWM mode of operation. (We show the 16-bit mode of operation, since that is what is used for the servo motor control application).
Figure 3. PWM mode, 16-bit, fixed frequency
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2.1.5 TCM mode control register
Each TCM has a mode control register (TCMCODEn) that is used to determine how the TCM functions. For a 16-bit fixed frequency PWM mode, bits E_COMP and PWM1 and PWM0 are set to a 1 while the other bits are left at 0. The E_COMP bit enables the comparator so that when there is a match between the 16-bit timer and the 16-bit compare registers, the CEXn pin is set (logic one). When the 16-bit timer overflows, the output is reset (logic zero). The PWM1 and PWM0 bits are used to enable the PWM mode with fixed frequency and the output going to the CEXn pin.
2.1.6 Compare, timer registers, and comparator
The capture compare registers (CAPCOMHn and CAPCOMLn) are part of the TCM and form a 16-bit register pair that is used to store a compare value. When the 16-bit comparator detects a match between the timer count (PCACHm/PCACLm) and the value in the compare registers (CAPCOMHn/CAPCOMLn), the CEXn pin is set (logic one). When the timer overflows, CEXn is reset (logic zero). Once the CAPCOM registers are written with a value, the resulting pulse width out on CEXn will continue to be the same cycle after cycle until a new value is written.
2.2 Programming the PCA for PWMProgramming the PCA for PWM requires selecting the clock source for the timer, setting the duty cycle for the pulse, and selecting the mode of operation.
2.2.1 Timer clock source
As was mentioned in Section 2.1, there are three options for the clock source. Either the internal clock (PCACLK0) divided down by a selectable divisor, Timer 0 overflow, or an external clock. Once it is determined which clock is necessary to provide the desired frequency, the clock select bits (CLKSEL1 and CLKSEL0) in the PCACON0 register should be programmed appropriately to select the desired clock source. If the internal clock is used, the prescaler bits (PCA0PS[3:0]) in the CCON2 register should be programmed appropriately.
2.2.2 Mode of operation
The PCA supports various modes of PWM operation, including 8-, 10-, and 16-bit fixed frequency. Additionally, there is an 8-bit mode with variable frequency (see data sheet for more details as this document focuses on the fixed frequency mode). The fixed frequency mode selected depends on the amount of resolution required for the duty cycle, the more bits, the higher the resolution.
The 10B_PWM bit in the PCACON0 register (10B_PWM) selects either the 10-bit or 16-bit PWM mode. Additionally, there are mode bits in the TCMMODEx register that determine how the respective TCM functions. The E_COMP bit in the TCMMODEx register enables the comparator that must be set for PWM operation. Also, the PWM[1:0] bits enable the 8-, or 10-/16-bit PWM mode of operation.
The MCU port 4 I/O pins are multifunctional and can be configured for a variety of functions. These I/O pins default to MCU I/O mode and must be configured using the special function registers (P4SFS0/1) for PWM output. The pin signal names, when used as PCA function,
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are called CEXx internally and TCMx externally. The output of a CEXn signal to a TCMx pin is configured on an individual basis as needed.
2.2.3 Duty cycle
The duty cycle is the time that the pulse is high with respect to the time that it is low. Before setting the duty cycle, it is important to understand how the hardware functions. Figure 4 shows a typical PWM waveform. When the timer count is 0 (as is when the timer is first started or after an overflow), the PWM output is a low. When the timer count matches the value in the CAPCOM register, the PWM output changes state to a high level. Then, when the timer overflows, it starts counting again from 0 and the PWM output changes state to a low level. By using different values in the CAPCOM register, the duty cycle is varied from 0% to 100%.
Figure 4. PWM mode of operation
So, to set the duty cycle, the appropriate value must be written to the CAPCOM register. In 10- and 16-bit mode, the CAPCOM register consists of two 8-bit registers (CAPCOMH0 and CAPCOML0) with the value being LSB justified for 10-bit mode (and the upper 6 bits in CAPCOMH0 not used). In 8-bit mode, just the CAPCOML0 register is used and CAPCOMH0 is ignored.
The value to write to CAPCOM register can be determined in the following way:
So, if we want a 20% duty cycle in 16-bit PWM mode, substituting numbers in the equation, we have:
[1 - (0.20)] * (65536) = (CAPCOM value) ≈ (52429)
For a 20% duty cycle in 10-bit mode, we have:
[1 - (0.20)] * (1024) = (CAPCOM value) ≈ (819)
And for a 20% duty cycle in 8-bit mode:
[1 - (0.20)] * (256) = (CAPCOM value) ≈ (205)
Note: The PWM output only changes states when there is a match of the timer count and the CAPCOM register. If the MCU writes a value to the CAPCOM register after the timer count
Timer OverflowMatch
(Timer andCAPCOM)
VCC
GND
period
dutycycle
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has passed that value, the PWM output will remain low for the entire current period. In the next period, the PWM output will go high when there is a match. To ensure there is no dead cycle, the CAPCOM register should be written with a new value either on a match or overflow. There are flags in the PCA status register (PCASTATA) that indicate when such events occur. For duty cycles near 0%, it is best to use the overflow flag. For duty cycles near 100%, the match flag is the best to use.
2.2.4 Starting the PCA to generate a PWM output signal
After the clock source has been selected, the mode bits set appropriately, the CAPCOM register written, and the I/O pins configured, the only thing left to do is to enable the PCA. To turn on, or enable the PCA requires setting the EN_PCA bit in the PCACON0 register. To turn off the PCA, just clear the EN_PCA bit.
If it is desired to have 4 to 6 PWM outputs with the periods in sync, then the EN_ALL bit in the PCACON0 register should be used to start PCA0 and PCA1 at the same time. This ensures that clock to each PCA is turned on at the same time so that they are in sync with each other.
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3 PWM software API
This describes a high-level C interface for basic PWM control and servo motor control in particular.
These API procedures support the six PCA I/O ports, allowing independent PWM operation on each of the ports. In addition, the API supports 8-, 10-, and 16-bit resolution for up to 16 PWM frequencies.
The constants, data types, prototypes and data structures needed by the application to use the API are declared in the following header files.
The API also uses the upsd3400.h and upsd3400_hardware.h header files to reference the DK3400 hardware registers. These header files is provided with both Keil and Raisonance development toolkits.
An application program using the API would typically have the following include statements.
The following sections describe each API procedure in detail.
3.1 Init_PWM
Init_PWM() Initialize and start PWM operation for a particular channel.Init_Servo_PWM() Initialize and start PWM operation for a particular channel that is
used for servo motor control.Update_PWM() Update the duty cycle for a channel already operating in PWM
mode.Disable_PWM() Disable PWM output for a particular channel.
upsd_pwm.h Appendix A: upsd_pwm.h PWM API declarations and prototypesupsd_type.h Appendix B: upsd_type.h PWM API data types
Description This initializes and starts PWM operation for the requested channel. The channel is set to the PWM mode resolution (8-, 10-, or 16-bit) at the frequency prescaler divisor index value (1-16), and the dutyCycle consistent with the specified mode. (The dutyCycle is a raw value with either 8-, 10-, or 16-bit significance).
When the PCA counter is equal to dutyCycle, the output pin for the channel transitions to high. The signal transitions to low when the PCA counter overflows.
Parameters channel - PCA I/O port corresponding to Timer Counter Module output pin.
Description This initializes and starts PWM operation for the requested channel. The PCA is configured for servo motor PWM operation. The channel is set to 16-bit counter resolution, a frequency of about 26msec and a duty cycle of 1.5msec.
Use Update_PWM() to change the duty cycle.
See also: 3.1: Init_PWM()
Parameters channel - PCA I/O port corresponding to Timer Counter Module output pin.
Description This updates the duty cycle for the requested channel. The dutyCycle is a raw value with either 8-, 10-, or 16-bit significance, depending on the current channel PWM mode resolution.
NOTE: A call to this procedure is not effective until the PCA counter overflows. Depending on the current PCA counter value, the dutycycle of the current period, only, may be longer or shorter than requested.
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3.4 Disable_PWM
Parameters channel - PCA I/O port corresponding to Timer Counter Module output pin.
Description This disables PWM output on the I/O pin associated with the channel. PCA registers are modified and PWM operation may be resumed by calling either Init_PWM() or Init_Servo_PWM().
Parameters channel - PCA I/O port corresponding to Timer Counter Module output pin.
Return SUCCESS - Channel disabled and PWM output stopped.
NOTE: PCA hardware registers are not reset.
FAILURE - Unable to disable requested channel.
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4 Servo motor control
The servo used in this example requires a control signal with a pulse width from 1.0 ms to 2.0 ms with 1.5 ms being the center (or neutral) position. The period of the control signal is not critical and is typically around 20 ms.
Since the uPSD3400 runs at a maximum frequency of 40 MHz, we will use this as our main clock for this discussion. Additionally, we will use the PCA in 16-bit PWM mode and use the internal clock, PCA0CLK, as the input clock to the PCA.
PCA0CLK is the main oscillator clock divided down by a firmware selectable value of 1 through 32,768 (by powers of two). Doing some calculations, we determine that selecting a divisor of 16 results in a 26.2 ms period. Even though the period is around 6 ms longer than what is typically used, the servo responds appropriately.
Substituting numbers, (40MHz clock and a clock divisor of 16), we get a period of:
(65536) * (1 / ((40 MHz) / 16)) = 26.2 ms
The PWM API includes a function that makes it easy to use the PCA for servo applications. This function is called Init_Servo_PWM() and it initializes the PCA for 16-bit, fixed frequency PWM with a period of 26.2 ms and also centers the servo at 0° by setting the duty cycle for a pulse width of 1.5 ms. In addition, it sets the respective port 4 pin to the PWM output mode based on the channel input parameter passed to the function.
4.1 Duty cycleSince we need to provide the servo with a control signal that has a pulse width between 1.0 ms and 2.0 ms, we need to determine the range of values to be written to the compare registers (CAPCOMH0 and CAPCOML0). Rather than make calculations based on duty cycle in percent, we will use actual time that we want the pulse width to be since that is the specification that we have. The equation to determine the CAPCOM value for a specific pulse width, as was presented earlier, is:
For a 1.0 ms pulse width, substituting in the numbers, we get:
[1 - ((1.0 ms) / (26.2 ms))] * (65536) ≈ 63035
For a 2.0 ms pulse width, substituting in the numbers, we get:
[1 - ((2.0 ms) / (26.2 ms))] * (65536) ≈ 60533
For a 1.5 ms pulse width, substituting in the numbers, we get:
[1 - ((1.5 ms) / (26.2 ms))] * (65536) ≈ 61784
So, to drive the servo motor to a -45° deflection, we provide a control signal with a pulse width of 1.0 ms by writing 63035 to the CAPCOM registers. To drive the servo motor to the +45° deflection, we write a value of 60533 to the CAPCOM registers resulting in a pulse width of 2.0 ms. To center the servo motor at 0°, we write a value of 61784.
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Once the PCA has been initialized with a call to the Init_Servo_PWM() function, the duty cycle is changed by calling the Update_PWM() function. Passed to this function is the channel number and the raw 16-bit value to write to the CAPCOM register.
If it is desired to disable PWM on a particular channel, the Disable_PWM() function will disable PWM specified channel.
4.2 API application exampleThe example provided with the API first initializes the servo setting it to the center position (1.5 ms pulse width). After a short delay, the servo is driven to the -45° position (1.0 ms pulse width), to the center (1.5 ms pulse width), to +45° (2.0 ms pulse width) and then back to the center. This cycle is repeated continuously. Listed below is a copy of the example code.
//Define some deflection points#define minus45deg 63035#define centerpos 61784#define plus45deg 60533
main(){
_returned_error_code status;
// setup operating environmentinit ();
status = Init_Servo_PWM(CHANNEL_1); // Initialize the PWM forservo control
// do forever ... while (1) {
mydelay (2);status = Update_PWM(CHANNEL_1, minus45deg); //-45 degree deflection (1.0 ms
pulse width)
mydelay (2);status = Update_PWM(CHANNEL_1, centerpos); //Center (1.5 ms pulse width)
mydelay (2);status = Update_PWM(CHANNEL_1, plus45deg); //+45 degree deflection (2.0 ms
pulse width)
mydelay (2);status = Update_PWM(CHANNEL_1, centerpos); //Center (1.5 ms pulse width)
}}
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5 Conclusion
The PCA in the uPSD3400, in combination with the API, provides an easy-to-use high level interface for controlling R/C Servo motors. With just over 11-bits (2502 total counts) of resolution for an encoded pulse width varying between 1.0ms and 2.0ms, an R/C servo motor's deflection can be controlled with approximately 0.036° per count (assuming the servo's total deflection range is 90°). This provides for very fine and smooth control of the servo motor with very satisfactory results.
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Appendix A upsd_pwm.h
/*************** (C) COPYRIGHT 2005 STMicroelectronics *************** File Name : upsd_pwm.h* Author : MCU Application Team* Date First Issued : 01/01/2005* Description : Header file for the uPSD ...********************************************************************** History:* 07/01/2005 : V1.0* 06/01/2005 : created*********************************************************************THE PRESENT SOFTWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH SOFTWARE AND/ OR THE USE MADE BY CUSTOMERS OF THE CODING INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.********************************************************************/#ifndef _upsd_pwm_H#define _upsd_pwm_H
/******** (C) COPYRIGHT 2005 STMicroelectronics *****END OF FILE****/
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Appendix B upsd_type.h
/*************** (C) COPYRIGHT 2005 STMicroelectronics *************** File Name : upsd_type.h* Author : MCU Application Team* Date First Issued : 01/01/2005* Description : Common data types********************************************************************** History:* 07/01/2005 : V1.0* 06/01/2005 : created*********************************************************************THE PRESENT SOFTWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH SOFTWARE AND/ OR THE USE MADE BY CUSTOMERS OF THE CODING INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.********************************************************************/#ifndef _upsd_type_H#define _upsd_type_H
typedef unsigned long u32;typedef unsigned short u16;typedef unsigned char u8;
typedef signed long s32;typedef signed short s16;typedef signed char s8;
/********* (C) COPYRIGHT 2005 STMicroelectronics *****END OF FILE****/
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Appendix C upsd_pwm.c
/******************** (C) COPYRIGHT 2005 STMicroelectronics ********************* File Name : upsd_pwm.c* Author : AMCU Application Team* Date First Issued : 01/01/2005* Description : ... for the uPSD ...******************************************************************************** History:* 06/08/2006 : V1.0* 06/01/2005 : created******************************************************************************* THE PRESENT SOFTWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME. AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT, INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH SOFTWARE AND/OR THE USE MADE BY CUSTOMERS OF THE CODING INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.*******************************************************************************/
/******************************************************************************** Function Name : Set_DutyCycle* Description : This function sets the dutycycle for a specific PWM channel.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* : mode - 8-, 10-, 16-bit* : dutyCycle - (actual CAPCOM value) 0-FF, 0-03FF or 0-FFFF* Output : None* Return : SUCCESS = dutyCycle successfully set* FAILURE = invalid channel id parameter*******************************************************************************/_returned_error_code Set_DutyCycle(CHANNEL_ID channel, PWM_MODE mode, u16 DutyCycle){
u8 dc_l;u8 dc_h;
dc_l = DutyCycle & 0x00ff;
if (mode == RES_8_BIT) // In 8-bit mode, the PWM reload value is stored in CAPCOMH0, dc_h = dc_l; // so load CAPCOMH0 and CAPCOML0 with the same value. else
/******************************************************************************** Function Name : Get_TCM* Description : This function returns the TCM mode for a specific PWM channel.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* Output : None* Return : current TCM mode; 8-, 10-, 16-bit (returns 0 on error)*******************************************************************************/u8 Get_TCM(CHANNEL_ID channel){
/******************************************************************************** Function Name : Set_PWMIO* Description : This function sets the PWM I/O signal function for a channel.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* Output : None* Return : SUCCESS = I/O signal function successfully set*******************************************************************************/_returned_error_code Set_PWMIO(CHANNEL_ID channel){
/******************************************************************************** Function Name : Init_PWM* Description : This function initializes and starts PCA operation for a * PWM channel.
/******************************************************************************** Function Name : Init_Servo_PWM* Description : This function the PCA initializes and starts the PCA subsystem * for servo motor PWM operation, for a specific channel.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* Output : None* Return : SUCCESS = channel ititialized* FAILURE = channel failed to initialize*******************************************************************************/_returned_error_code Init_Servo_PWM(CHANNEL_ID channel){
// for now use prescalar = 16 (freq = 26.2 msec); dutycycle = 1.5msecreturn (Init_PWM(channel, RES_16_BIT, 4, 61784));
* Function Name : Disable_PWM* Description : This function disables PWM operations for a specific PWM* channel. If the channel is already disabled, this has no* effect.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* Output : None* Return : SUCCESS = PWM operations for channel disabled* FAILURE = Invalid parameter or unable to handle request* (channel state undefined)*******************************************************************************/_returned_error_code Disable_PWM(CHANNEL_ID channel){
_returned_error_code status;CH_CTL *ch_p;u8 mode;
status = SUCCESS;
// disable selected channel and update control block
if ((channel >= CHANNEL_1) && (channel <= CHANNEL_6)){
/******************************************************************************** Function Name : Update_PWM* Description : This function updates the PWM duty cycle. It updates the* specified channel according to how the channel is initialized* (standard/servo, mode). The change is effective on the next* PCA counter cycle.* Input : channel - 'CHANNEL_1', 'CHANNEL_2', ... 'CHANNEL_6'* dutyCycle - 8- or 16-bitvalue, depending on channelmode/type* Output : None* Return : SUCCESS = PWM operation mode successfully set* FAILURE = Invalid parameter or unable to handle request;* (channel state undefined)*******************************************************************************/_returned_error_code Update_PWM(CHANNEL_ID channel, u16 dutyCycle){
_returned_error_code status;CH_CTL *ch_p;
// update duty cycle based on channel configuration
if ((channel >= CHANNEL_1) && (channel <= CHANNEL_6)){
ch_p = &ch_ctl_blk[channel];
if (((ch_p->mode == RES_8_BIT) && (dutyCycle < 256)) ||
/******************* (C) COPYRIGHT 2005 STMicroelectronics *****END OF FILE****/
Revision history AN2283
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6 Revision history
Date Revision Changes
16-Jun-2006 1.0 Initial release.
AN2283 Revision history
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