PWM communication between two dsPIC - Revision history

LubinKerhuel at 21:39, 14 February 2011

2011-02-14T21:39:29Z

LubinKerhuel: /* Bootloader RESET */

2011-02-14T00:59:01Z

Bootloader RESET

LubinKerhuel at 00:58, 14 February 2011

2011-02-14T00:58:01Z

LubinKerhuel at 00:51, 14 February 2011

2011-02-14T00:51:55Z

LubinKerhuel: /* Characteristics of PWM transmissions */

2011-02-14T00:51:10Z

Characteristics of PWM transmissions

LubinKerhuel: /* Model (A): Emission */

2011-02-14T00:40:47Z

Model (A): Emission

LubinKerhuel: /* Model (A): Emission */

2011-02-14T00:38:24Z

Model (A): Emission

LubinKerhuel at 00:30, 14 February 2011

2011-02-14T00:30:00Z

LubinKerhuel: /* Model B: Reception */

2011-02-14T00:28:27Z

Model B: Reception

LubinKerhuel: /* Sine wave generation */

2011-02-14T00:24:13Z

Sine wave generation

@@ Line 75: / Line 75: @@
 Value 55 will stop the dsPIC (and will prevent the dsPIC from using its UART anymore). Then value 66 reset the dsPIC which will enter into its embedded bootloader code. Then the PC bootloader and the dsPIC bootloader application should see each other.
-==Model (A): Emission ==
+==Model A: Emission ==
 [[Image:SimulinkModel_PWM_a_30f4012.png|thumb|right|350px|Simulink model A: PWM_a_30f4012]]

@@ Line 69: / Line 69: @@
 ===Bootloader RESET===
-[[Image:SimulinkModel_BootloaderResetSubsystem.png|thumb|left|300px|Bootloader Reset subsystem. The subsystem read one value received on the UART. If it receive the value 55, another subsystem is enabled. This subsystem will block the step until a character 66 is received on the UART, causing a reset of the chip (see subsystems).]]
+[[Image:SimulinkModel_BootloaderResetSubsystem.png|thumb|right|357px|Bootloader Reset subsystem. The subsystem read one value received on the UART. If it receive the value 55, another subsystem is enabled. This subsystem will block the step until a character 66 is received on the UART, causing a reset of the chip (see subsystems).]]
 Both models use UART to exchange data with the PC. The block [[Block/UART_Configuration|UART configuration] set-up the dsPIC UART1 peripheral on Alt Tx/Rx pins with a bauds rate of 115200. dsPIC A does not send result to the PC, but use however the UART for the bootloader. The subsystem Bootloader RESET (tinybld) read the received data on the UART. If the value 55 is received, the subsystem will wait forever (and thus stop the real time computation of the model steps), until the value 66 is received on the UART. The dsPIC is then reset. Thus, from the PC tinybld bootloader application (tinybldWin.exe), the values 55 and 66 are sent first to reset the dsPIC (theses reset code are set up in the Option tab, in Codes to sent first).
 Value 55 will stop the dsPIC (and will prevent the dsPIC from using its UART anymore). Then value 66 reset the dsPIC which will enter into its embedded bootloader code. Then the PC bootloader and the dsPIC bootloader application should see each other.
-−
 ==Model (A): Emission ==
 [[Image:SimulinkModel_PWM_a_30f4012.png|thumb|right|350px|Simulink model A: PWM_a_30f4012]]

@@ Line 41: / Line 41: @@
 =Electronics=
-[[Image:Circuit_PWM.png|thumb|right|350px|PWM Circuit]]
+[[Image:Circuit_PWM.png|thumb|left|350px|PWM Circuit]]
 The prototyping board comprises two microcontrollers dsPIC30f4012. Each dsPIC is clocked with a 10MHz quartz and each dsPIC has a led connected to a [[Block/Digital_Output_Write|digital output port]] (RB0). The dsPIC at the bottom of the board (noted A) generate a PWM signal on the PWM1L pin (26). The dsPIC at the top of the board (noted B) measure PWM signal characteristics through its Input Capture pin (15). Thus the green wire connects the dsPIC A PWM1L pin (26) to the dsPIC B IC1 pin (15). Both dsPIC already share the ground signal through their alimentation.
@@ Line 69: / Line 69: @@
 ===Bootloader RESET===
 Both models use UART to exchange data with the PC. The block [[Block/UART_Configuration|UART configuration] set-up the dsPIC UART1 peripheral on Alt Tx/Rx pins with a bauds rate of 115200. dsPIC A does not send result to the PC, but use however the UART for the bootloader. The subsystem Bootloader RESET (tinybld) read the received data on the UART. If the value 55 is received, the subsystem will wait forever (and thus stop the real time computation of the model steps), until the value 66 is received on the UART. The dsPIC is then reset. Thus, from the PC tinybld bootloader application (tinybldWin.exe), the values 55 and 66 are sent first to reset the dsPIC (theses reset code are set up in the Option tab, in Codes to sent first).

@@ Line 1: / Line 1: @@
 =Description=
-This example shows how one variable is transmitted from one microcontroller to another throw a PWM signal. A Sinus is generated in the bottom microcontroller (A). Values are sent with a 1 kHz rate to the microcontroller (B) through a PWM signal. Microcontroller B reconstructs the received value sent the result to the PC with its UART peripheral. The Matlab rs232gui interface can then plot the received values.
+This example shows how one variable is transmitted from one microcontroller to another throw a PWM signal. A Sinus is generated in the microcontroller (A). Values are sent with a 1 kHz rate to the microcontroller (B) through a PWM signal. Microcontroller B reconstructs the received value sent the result to the PC with its UART peripheral. The Matlab rs232gui interface can then plot the received values.
 (This example is not an Amplitude Modulation (AM) based on a low pass filtered PWM high frequency signal)

@@ Line 5: / Line 5: @@
 =Characteristics of PWM transmissions=
-[[Image:Scope_HM205_PWM_01.jpg|thumb|right|350px|Scope picture of a PWM Signal with a large duty cycle]]
+[[Image:Scope_HM205_PWM_01.jpg|thumb|right|350px|Scope picture of a PWM Signal generated by the microcontroller (A), here a large duty cycle code for a large value]]
-[[Image:Scope_HM205_PWM_02.jpg|thumb|right|350px| Scope picture of a PWM Signal with a small duty cycle]]
+[[Image:Scope_HM205_PWM_02.jpg|thumb|right|350px|Scope picture of a PWM Signal generated by the microcontroller (A), here a small duty cycle code a small value]]
 Pulse Width Modulation (PWM) or Pulse Duration Modulation (PDM) signals are a two state signal (square or digital) with a fixed frequency and whose [http://en.wikipedia.org/wiki/Pulse-width_modulation duty cycle] can vary.
@@ Line 38: / Line 38: @@
 We note however that information transmitted through a PWM signal is robust to electrical noise because it is based on a temporal coding.
 Received value may be received with a delay.
-−
 =Electronics=
 [[Image:Circuit_PWM.png|thumb|right|350px|PWM Circuit]]

@@ Line 83: / Line 83: @@
 Matlab 2010b is used here. 3 methods tested belong to the Simulink standard library. 1 method belongs to the Signal Processing Blockset.
 The 4 presented sine generations are simulated in the simulink model Sinus_Generation_Simulation.mdl configured with a fixed time step of 1ms. Precision of theses 4 sine wave generator are compared using this simulation. Then, the sine wave comprised within the model PWM_a_30f4012.mdl were successively replace with each sine wave generator. The model ROM consumption is given by the compiler. A block [[Block/Calculus_Time_Step|Calculus Time Step]] connected to a block [[Block/Tx_Output_Multiplexed_For_Matlab-Labview|Tx_Labview_Matlab]] provide a precise numerical value of the time resources taken by the model step (these values were averaged on several seconds).
 [[Image:SimulinkModel_SinusOptimisation.png|thumb|right|350px|Model:Sinus_Generation_Simulation. Comparison of different method for sinus generation including Cordic and lookup table.]]

@@ Line 83: / Line 83: @@
 Matlab 2010b is used here. 3 methods tested belong to the Simulink standard library. 1 method belongs to the Signal Processing Blockset.
-[[Image: SimulinkModel_MesuringTimeStep.png|thumb|right|305px|Measuring Time Step]]
+[[Image: SimulinkModel_MesuringTimeStep.png|left|305px|Measuring Time Step]]
 The 4 presented sine generations are simulated in the simulink model Sinus_Generation_Simulation.mdl configured with a fixed time step of 1ms. Precision of theses 4 sine wave generator are compared using this simulation. Then, the sine wave comprised within the model PWM_a_30f4012.mdl were successively replace with each sine wave generator. The model ROM consumption is given by the compiler. A block [[Block/Calculus_Time_Step|Calculus Time Step]] connected to a block [[Block/Tx_Output_Multiplexed_For_Matlab-Labview|Tx_Labview_Matlab]] provide a precise numerical value of the time resources taken by the model step (these values were averaged on several seconds).
 * The classical sine wave source block in Simulink/Sources is the most precise. However, the computational time of this block is important (21% of the 1ms time step). It uses a moderate ROM size (7%).
@@ Line 107: / Line 108: @@
 Thus, the +-5000 amplitude sinus values are translated within 5% and 95% of the PWM value. The resulting translated value will code directly the duty cycle. Thus, the PWM signal duty cycle is modulated within the range 5% and 95% and the PWM signal is never constant.
-−
 ==Model B: Reception==
 [[Image:SimulinkModel_PWM_b_30f4012.png|thumb|right|350px|Simulink model B: PWM_b_30f4012]]

@@ Line 109: / Line 109: @@
 ==Model B: Reception==
-[[Image:SimulinkModel_PWM_b_30f4012.png|thumb|right|350px|Simulink model A: PWM_b_30f4012]]
+[[Image:SimulinkModel_PWM_b_30f4012.png|thumb|right|350px|Simulink model B: PWM_b_30f4012]]
 The model B read the PWM signal duty cycle and reconstructs the original variable sent. Then, the microcontroller B sent the variable through the [[Block/Tx_Output_Multiplexed_For_Matlab-Labview|Tx Output Multiplexed for Matlab]] on the UART peripheral. The reconstructed sine wave can then be traced using the blockset internal [[Block/Interface_Tx-Matlab|rs232gui]] tool.
@@ Line 117: / Line 117: @@
 In this example, the PWM is created with a high resolution (15 bits) and read with a high resolution also (14 bits). Consequently, we obtain a pretty good transmission with no quantization errors. The PWM period is equal to the model time step. Thus the delay at the receiver side may vary between 0 time steps in certain condition to 4 time step (4 ms) in the worst case. Using a smaller PWM period (for example a period corresponding to a half time step) may limit the max delay to 1 time step while it will also reduce the resolution of the overall transmission.