28020

599 Menlo Drive, Suite 100 Rocklin, California 95765, USA Office: (916) 624-8333 Fax: (916) 624-8003 General: info@parallax.com Technical: support@parallax.com Web Site: www.parallax.com Educational: www.stampsinclass.com PWMPAL (#28020) PWM Generation, Control, and Background Counting Introduction The PWMPAL is an intelligent peripheral that adds up to four PWM output channels and up to four control/counter input channels to the 24-pin versions of the BASIC Stamp® microcontroller. PWM channels can be configured to operate under software control, or under hardware control through the corresponding counter input channel. In addition to PWM waveform generation, the PWMPAL has four 16-bit counters that operate at all times, even when the counter pin is used for hardware PWM control. Communication with the PWMPAL is handled through a bi-directional serial connection on pin P0 of the microntroller module. The Parallax AppMod communications protocol is used, allowing baud rates of 9600, 19,200 and 38,400 baud. Examples of PWMPAL Uses: • • • Servo or DC motor control for robotics and animatronics AC waveform (square wave) generation for bi-color LEDs and sensors Background counting for process control, robotic motion monitoring, etc. Packing List Verify that your PWMPAL kit is complete in accordance with the list below: • • PWMPAL "Smart Socket" module Documentation Note: PWMPAL demonstration software files may be downloaded from www.parallax.com. Features • • • • • • • Up to four simultaneous PWM outputs Independent control of each PWM output high-time, low-time, and phase Generate frequencies from 0.3 Hz to 20 kHz; duty cycle independent * Outputs may operate under software or hardware control Up to four 16-bit counters Auto-baud detection (9600, 19.2K, 38.4K) for Host-to-PWMPAL communications Requires no PCB "real estate" – mounts underneath microcontroller module * Duty cycle independence is not available for the entire range of output frequencies © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 1 Connections Since the PWMPAL mounts directly beneath a 24-pin microcontroller module, the connections are automatic. Before installing the PWMPAL, you should perform the following steps: 1. Clear the current BASIC Stamp microcontroller program to ensure that all pins are set to inputs. The simplest program to do this contains just one statement: END 2. 3. 4. 5. 6. Disconnect power from the BASIC Stamp microcontroller circuit. Remove the BASIC Stamp microcontroller from its socket. Install the PWMPAL in the 24-pin socket, noting the position of pin 1 (marked with dot). Install the BASIC Stamp microcontroller in the PWMPAL socket. Reconnect power to the circuit and program the BASIC Stamp microcontroller as desired. The table below lists the PWMPAL / BASIC Stamp pin sharing connections: Pin P0 P8 P9 P10 P11 P12 P13 P14 P15 PWMPAL Function Serial link between BASIC Stamp / PWMPAL Counter 1 input / Motor 1 HW control Counter 2 input / Motor 2 HW control Counter 3 input / Motor 3 HW control Counter 4 input / Motor 4 HW control Motor 1 output Motor 2 output Motor 3 output Motor 4 output Dedicated Yes No No No No No No No No As noted in the table above, the only pin dedicated to the PWMPAL is P0. This pin serves as the serial link between the PWMPAL and host microcontroller. The PWMPAL pins connected to pins P8 – P11 are always configured as inputs, so there is no conflict and the host may use P8 – P11 as inputs or outputs as the program requires. For pins P12 – P15 the programmer must use caution to prevent conflict between the host and the PWMPAL. Note: The PWMPAL module has current-limiting resistors on its motor output lines to prevent a conflict from damaging either the PWMPAL or the host microcontroller. Still, the programmer should exercise caution. When any of the PWMPAL motor control outputs are enabled the associated host pin(s) should be set to input mode. How It Works Using a small coprocessor, the PWMPAL receives serial commands from the host microcontroller, then configures and controls the PWMPAL I/O pins as directed. The PWMPAL "motor" control outputs will be a TTL level square wave. The frequency and period of this waveform is determined by control values sent to the PWMPAL from the host. Figure 1 shows the PWM output waveform. © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 2 Figure 1 – PWM Output The PWMPAL gives the program control of the on- and off-time values, hence giving control of the output frequency and duty cycle. In the PWMPAL, the on and off times are specified with 16-bit values in units of 25 microseconds (0.000025 seconds). Using the formula: Frequency = 1 / Period the minimum and maximum output frequencies of the PWMPAL can be calculated. Given the minimum and maximum values for on- and off-time: Frequency (max) = 1 / ((1 x 0.000025) + (1 x 0.000025))  1 / 0.00005 = 20,000 Hz Frequency (min) = 1 / ((65535 x 0.000025) + (65535 x 0.000025))  1 / 3.27675 = 0.30518 Hz Duty Cycle describes the relationship between the on-time and the total period in terms of percent. With full control of the on- and off-time values, the programmer can set the frequency and duty cycle as required. If, for example, the desired PWM output was 1000 Hz with duty cycle of 40%, the following steps would be used to calculate the on-time and off-time values: 1. Determine the waveform period (1 / Frequency): 1 / 1000 = 0.001 2. Determine the PWMPAL units in the period: 0.001 / 0.000025 = 40 3. For the on-time, multiply the total period units by the desired duty cycle: 40 x 0.4 = 16 4. For the off-time, subtract the on-time units from the total period units: 40 – 16 = 24 See the following sections for specifics on sending PWM on- and off-time values to the PWMPAL. © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 3 PWMPAL Commands All PWMPAL commands (except ID, see below) follow the Parallax AppMod serial protocol and will begin with the string: "!PWM" The "!" is used for synchronization and baud rate detection; the "PWM" identifies the device type. What follows will generally be a command letter and unit identifier. "ID" Request PWMPAL ID String Use: SEROUT 0, baud, ["!ID] SERIN 0, baud, [STR version\3] baud version variable or constant value for 9600, 19.2K, or 38.4K baud (host-dependent value ) 3-byte array to hold version string The "!ID" command requests the PWMPAL ID string (three ASCII characters). Note that this command does not follow the standard AppMod protocol by specifying the device type in the command string, so it should NOT be used on the same serial connection as other AppMod devices. "Mn" Set PWM Motor Timing Control Values Use: SEROUT 0, baud, ["!PWMMx", tOn.BYTE0, tOn.BYTE1, tOff.BYTE0, tOff.BYTE1] baud n tOn tOff variable or constant value for 9600, 19.2K, or 38.4K baud "1" to "4" – specifying the PWMPAL output channel (P12 – P15) variable or constant for on-time; in 25 microsecond units variable or constant for off-time; in 25 microsecond units The "Mn" command sets the on- and off-time values for a specified PWM channel. Note that the 16-bit on- and off-time values must be transmitted as bytes, low-byte first. Example (Baudmode value for BS2 microcontroller ): SEROUT 0, 6, ["!PWMM1", 2, 0, 6, 0] The example above configures PWM channel 1 (P12) to have an output frequency of 5000 Hz with a duty cycle of 25%. It is important to note that setting the on- and off-time values does not enable the PWM output channel if it was previously disabled. This is handled separately through the Set Status command (see below). Finally, there is a special-case use of the "Mn" command: "M0". For example: SEROUT 0, 6, ["!PWMM0"] The purpose of this command is to disable all PWM output channels; returning all to a Hi-Z state. © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 4 "SS" Set Motor Control/Status Byte Use: SEROUT 0, baud, ["!PWMSS", status] baud status variable or constant value for 9600, 19.2K, or 38.4K baud variable or constant value; PWMPAL status bits (see table below) The "SS" command sets the control/status byte to the PWMPAL. The purpose of this byte is to enable or disable PWMPAL channel outputs and to set the type of control (software or hardware). The low nibble of the control/status byte holds the control bits; the upper nibble holds the output PWM channel enable bits. Control/Status Byte Definitions: Bit 0 1 2 3 4 5 6 7 Purpose M1 Control M2 Control M3 Control M4 Control M1 Status M2 Status M3 Status M4 Status When 0 Software Software Software Software Disabled Disabled Disabled Disabled control control control control When 1 Hardware control Hardware control Hardware control Hardware control Enabled * Enabled * Enabled * Enabled * (P8) (P9) (P10) (P11) * When a PWM channel is enabled and set for hardware control, the associated hardware control input pin must be high before the PWM output will be active. Example: SEROUT 0, 6, ["!PWMSS", %00010000] The example above enables PWM output channel 1 (P12). The PWM output will begin immediately with the frequency and duty cycle as set with the "Mn" command. To change the output to hardware control, send the following: SEROUT 0, 6, ["!PWMSS", %00010001] Now the PWM output channel 1 (P12) will only be active when control channel 1 (P8) is high. "GS" Get Motor Control/Status Byte Use: SEROUT 0, baud, ["!PWMGS"] baud variable or constant value for 9600, 19.2K, or 38.4K baud The "GS" command will cause the PWMPAL to return the current control/status byte. After sending this command the BASIC Stamp must use SERIN to retrieve the control/status byte. Example: SEROUT 0, 6, ["!PWMGS"] SERIN 0, 6, [status] © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 5 "SP" Set Counter Enable/Motor Phase Byte Use: SEROUT 0, baud, ["!PWMSP", phase] baud phase variable or constant value for 9600, 19.2K, or 38.4K baud variable or constant value; PWMPAL counter/phase bits The "SP" command transmits the counter/phase byte to the PWMPAL. The purpose of this byte is to enable or disable PWMPAL counter channels and to set the phase of the PWM channels. (start low or start high). The lower nibble the counter/phase byte holds the counter enable bits; the upper nibble holds the output PWM channel phase bits. Counter/Phase Byte Bit Definitions: Bit 0 1 2 3 4 5 6 7 * Purpose C1 Control C2 Control C3 Control C4 Control M1 Phase M2 Phase M3 Phase M4 Phase When 0 Disabled Disabled Disabled Disabled Output starts Output starts Output starts Output starts When 1 Enabled * Enabled * Enabled * Enabled * Output starts Output starts Output starts Output starts low low low low high high high high Counters inputs may also be used as motor control inputs. In this application, the PWMPAL will count the number of times the PWM output was enabled (input = High). Example: SEROUT SEROUT SEROUT SEROUT 0, 0, 0, 0, 6, 6, 6, 6, ["!PWMM3", ["!PWMM4", ["!PWMSP", ["!PWMSS", $4D, $01, $4D, $01] $4D, $01, $4D, $01] %10000001] %11000000] ' ' ' ' 60 Hz, 50% 60 Hz, 50% set phase, enable PWM DC DC counter 1 enabled outputs This example sets PWM channels 3 (P14) and 4 (P15) to a 60 Hz, 50% duty-cycle output of opposite phase (P14 is high when P15 is low and vice-versa). Counter channel 1 is also enabled (line 3 of the code). Finally, the outputs are enabled under software control. "GP" Get Counter Enable/Motor Phase Byte Use: SEROUT 0, baud, ["!PWMGP"] baud variable or constant value for 9600, 19.2K or 38.4K baud The "GP" command will cause the PWMPAL to return the current counter enable/motor phase byte. After sending this command the BASIC Stamp must use SERIN to retrieve the counter/phase byte. Example: SEROUT 0, 6, ["!PWMGP"] SERIN 0, 6, [phase] © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 6 "Cn" Get Counter Value Use: SEROUT 0, baud, ["!PWMCn"] baud n variable or constant value for 9600, 19.2K, or 38.4K baud "1" to "4" – specifying the PWMPAL counter channel (P8 – P11) The "Cn" command will cause the PWMPAL to return the current value of the specified counter channel. After sending this command the BASIC Stamp must use SERIN to retrieve the counter data. Example: SEROUT 0, 6, ["!PWMC1"] SERIN 0, 6, [cntr1.LOWBYTE, cntr1.HIGHBYTE] ' get counter 1 ' receive value By using "C0" the value of all counters will be returned. The SERIN function must be setup to receive eight bytes when "C0" is used. "Xn" Clear Counter Value Use: SEROUT 0, baud, ["!PWMXn"] baud n variable or constant value for 9600, 19.2K, or 38.4K baud "1" to "4" – specifying the PWMPAL counter channel (P8 – P11) The "Xn" command will cause the PWMPAL to clear (reset to zero) the specified counter channel value. Example: SEROUT 0, 6, ["!PWMX1"] ' clear counter 1 By using "X0" the value of all counters will be reset to zero. Programming the PWMPAL The examples that follow will demonstrate how easy the PWMPAL is to program. The programmer must keep in mind, however, that using BASIC Stamp microcontroller pins P12 – P15 as outputs should be done with extreme caution as there could be a conflict with the PWMPAL that leads to unpredictable results. Design your code carefully so that PWMPAL outputs do not conflict with host outputs on these pins. © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 7 Example 1 – PWMPAL Programming Template For advanced programs a template is often useful to keep organized and prevent errors. This template file contains useful constant and variable values for programs that utilize the PWMPAL. Conditional compilation defintions allow this program to work properly with all BS2-family modules. ' ========================================================================= ' ' File....... PWMPAL_Template.BS2 ' Purpose.... Template for PWMPAL Programs ' Author..... Parallax ' E-mail..... support@parallax.com ' Started.... ' Updated.... 09 FEB 2005 ' ' {$STAMP BS2} ' {$PBASIC 2.5} ' ' ========================================================================= ' -----[ Program Description ]--------------------------------------------' -----[ Revision History ]-----------------------------------------------' -----[ I/O Definitions ]------------------------------------------------PpPin PIN 0 ' PWMPAL Serial I/O ' -----[ Constants ]------------------------------------------------------#SELECT $STAMP #CASE BS2, BS2E, BS2PE T9600 CON 84 T19K2 CON 32 T38K4 CON 6 #CASE BS2SX, BS2P T9600 CON 240 T19K2 CON 110 T38K4 CON 45 #ENDSELECT PpBaud CON T38K ' -----[ Variables ]------------------------------------------------------chan status phase VAR VAR VAR Nib Byte Byte ' channel number ' control/status ' counters/phase onTime offTime counter VAR VAR VAR Word Word Word ' work variable ' work variable ' work variable © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 8 m1Ctrl m2Ctrl m3Ctrl m4Ctrl m1Enable m2Enable m3Enable m4Enable VAR VAR VAR VAR VAR VAR VAR VAR status.BIT0 status.BIT1 status.BIT2 status.BIT3 status.BIT4 status.BIT5 status.BIT6 status.BIT7 ' status bits c1Enable c2Enable c3Enable c4Enable m1Phase m2Phase m3Phase m4Phase VAR VAR VAR VAR VAR VAR VAR VAR phase.BIT0 phase.BIT1 phase.BIT2 phase.BIT3 phase.BIT4 phase.BIT5 phase.BIT6 phase.BIT7 ' phase bits ' -----[ EEPROM Data ]----------------------------------------------------' -----[ Initialization ]-------------------------------------------------Setup: ' -----[ Program Code ]---------------------------------------------------Main: END ' -----[ Subroutines ]----------------------------------------------------- © Parallax, Inc. • PWMPAL (#28020) • 02/2005 Page 9 Example 2 – PWM Output with Hardware Control This example uses an active-high pushbutton circuit to control a DC motor connected to the PWM channel specified by the MotorNum constant. When the switch is pressed, the motor speed will ramp from 25% (minimum speed to get test motor moving) to 100% (full speed). When the switch is released the motor will stop – without having to send a new speed value to the PWM channel. This program shows how the BASIC Stamp microcontroller can monitor and use the control inputs. ' ========================================================================= ' ' File....... PWMPAL_Simple_Motor.BS2 ' Purpose.... Simple DC motor control – with hardware input control ' Author..... Parallax ' E-mail..... support@parallax.com ' Started.... ' Updated.... 09 FEB 2005 ' ' {$STAMP BS2} ' {$PBASIC 2.5} ' ' ========================================================================= ' -----[ Program Description ]--------------------------------------------' Demonstrates simple DC motor control with the PWMPAL. ' NOTE: Do NOT connect a DC motor directly to the PWMPAL / micro. You ' must use a buffer (transistor, MOSFET, etc.) to switch the current ' required by the motor. ' -----[ I/O Definitions ]------------------------------------------------PpPin SpdCtrl PIN PIN 0 8 © Parallax, Inc. • PWMPAL (#28020) • 02/2005 ' PWMPAL Serial I/O ' speed button Page 10 ' -----[ Constants ]------------------------------------------------------MotorNum CON 1 ' PWMPAL motor output #SELECT $STAMP #CASE BS2, BS2E, BS2PE T9600 CON 84 T19K2 CON 32 T38K4 CON 6 #CASE BS2SX, BS2P T9600 CON 240 T19K2 CON 110 T38K4 CON 45 #ENDSELECT PpBaud CON T38K Yes MinSpeed CON CON 1 25 ' minimum DC to spin motor ' -----[ Variables ]------------------------------------------------------speed status VAR VAR Byte Byte ' speed, 0% to 100% ' motor control status onTime offTime VAR VAR Word Word ' PWM timing ' -----[ Program Code ]---------------------------------------------------Main: DO IF (SpdCtrl = Yes) THEN IF (speed < 100) THEN speed = speed + 1 MIN MinSpeed GOSUB Set_Speed ENDIF ELSE speed = 0 ENDIF DEBUG HOME, "Speed = ", DEC speed, CLREOL PAUSE 100 LOOP ' ' ' ' button pressed can we speed up? increase speed update PWMPAL ' show current speed ' speed ramp delay ' -----[ Subroutines ]----------------------------------------------------Set_Speed: IF (speed = 100) THEN onTime = $FFFF offTime = $0001 ELSE onTime = speed offTime = 100 - speed ENDIF © Parallax, Inc. • PWMPAL (#28020) • 02/2005 ' full on for 100% ' set duty cycle Page 11 SEROUT PpPin, PpBaud, ["!PWMM", (48 + MotorNum), onTime.BYTE0, onTime.BYTE1, offTime.BYTE0, offTime.BYTE1] status.HIGHNIB = %0001