AN519. Implementing a Simple Serial Mouse Controller INTRODUCTION THEORY OF OPERATION FUNCTIONAL BLOCKS OF A SERIAL MOUSE

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1 Implementing a Simple Serial Mouse Controller INTRODUCTION The mouse is becoming increasingly popular as a standard pointing data entry device. There is no doubt that the demand for the mouse is increasing. Various kinds of mice can be found in the market, including optical mice, opto-mechanical mice, and their close relative, trackballs. The mouse interfaces to the host via a dedicated interface card or an RS-232 port. Their mechanisms are very similar. The major electrical components of a mouse are: Microcontroller Photo-transistors Infrared emitting diode Voltage conversion circuit The intelligence of the mouse is provided by the microcontroller, therefore the features and performance of a mouse is greatly related to the microcontroller used. This application note describes the implementation of a serial mouse using the PIC6C54. The PIC6C54 is a high speed 8-bit CMOS microcontroller offered by It is an ideal candidate for a mouse controller. THEORY OF OPERATION A mouse can be divided into several functional blocks: Microcontroller Button detection Motion detection RS-232 signal generation 5V DC power supply unit A typical functional block diagram is shown in Figure. In Figure 2, three pushbuttons are connected to the input ports of the PIC6C54. When a switch opening or closure is detected, a message is formatted and sent to the host. The X and Y movements are measured by counting the pulses generated by the photo-couplers. In the case of an opto-mechanical mouse, the infrared light emitted by the infrared diode is blocked by the rotating wheel, so that the pulses are generated on the photo-transistor side. In case of an optical mouse, the infrared light emitted by the infrared diode is reflected off the reflective pad patterned with vertical and horizontal grid lines. It is then received by the photo-transistor in the mouse. When any X or Y movement is detected, a message is formatted and sent to the host. FIGURE : FUNCTIONAL BLOCKS OF A SERIAL MOUSE Quadrature Encoders 2 RS-232 Port of Host Microcontroller 2 -V DC Power Conversion Circuitry +5V DC Pushbuttons 997 DS59C-page

2 The Microsoft Mouse System and the Mouse Systems device both use serial input techniques. The Mouse System protocol format contains five bytes of data. One byte describes the status of three push buttons, two bytes for the relative X movements and two bytes for the relative Y movements. The Microsoft protocol format contains three bytes of data describing the status of two push buttons and the relative X and Y movements. The details of these protocols are given in Table. Three lines are connected to the host via the RS-232 port: Signal Ground Received Data Request to Send Received Data carries the message sent by the mouse. While Request to Send provides a VDC for voltage conversion circuitry. A voltage of +5 VDC is required for electronic components inside the mouse, however, +5 VDC is not part of an RS-232 port, so voltage conversion circuitry is required. This circuit is typically composed of a 555 timer, Zener diodes, and capacitors. An example circuit is shown in Figure 3. Since the current supplied through the RS-232 port is limited to ma, the mouse cannot be designed to consume more than ma current unless an external power supply is provided. The PIC6C54, running at 4 MHz ( µs instruction cycle) can provide a very high tracking speed. An 8 MHz version of PIC6C54 is also available if higher performance is desired. FIGURE 2: PIC6C54 PIN ASSIGNMENTS +5 VDC OSC OSC2 RB RA RA YCLOCK YDATA Signals From Y-Coord. Photo-Transistor RB RB2 RA2 RA3 XCLOCK XDATA Signals From X-Coord. Photo-Transistor VDD MCLR RB7 GND Received Data Pin of Host RS-232 Port FIGURE 3: VOLTAGE CONVERSION CIRCUITRY 7 4 Signal RESET GND Vcc 8 Output Discharge 3 7 6k k -V to V V to +V RS-232 Port 555 RTS 2 Threshold Trigger 6 2 µf 5k +5 VDC Output 33 µf.5 µf DS59C-page 2 997

3 ABOUT THE SOFTWARE The major tasks performed by the software are button scanning, X and Y motion scanning, formatting and sending serial data to the host. These tasks need to be performed in parallel in order to gain better tracking speed. The pulses generated by the photo-couplers are counted while transmitting the serial signals to the RS-232 port. The number of pulses reflects the speed of the movement. The more pulses, the faster the movement. The directions of movement are determined by the last states and the present states of the outputs of the photo-transistors. In Figure 4, XCLOCK and XDATA are outputs from the photo-transistors corresponding to the X-axis movement. XDATA is read when a rising or a falling edge of XCLOCK is detected. For right movement, XDATA is either LOW at the rising edge of XCLOCK or HIGH at the falling edge of XCLOCK. The up and down movement detections follow the same logic. In Table, X7:X are data for relative movement. If X is positive, it implies that the mouse is moving to the right. If X is negative, it implies a movement to the left. Similarly, if Y is positive, it indicates that the mouse is moving down and if Y is negative, it indicates that the mouse is moving up. The pulses generated by the photo-couplers are checked before every bit is sent. A bit takes /2 second to send, if the distance between the grid lines is mm, the tracking speed will be up to 2 mm/second. FIGURE 4: VOLTAGE CONVERSION CIRCUITRY XCLOCK (XC) XDATA (XD) MOVE RIGHT MOVE LEFT YCLOCK (YC) YDATA (YD) MOVE UP MOVE DOWN TABLE : MOUSE SYSTEM AND MICROSOFT PROTOCOLS Mouse System Format* Microsoft Format* Bit Position Byte L M R L R Y7 Y6 X7 X6 Byte 2 X7 X6 X5 X4 X3 X2 X X X5 X4 X3 X2 X X Byte 3 Y7 Y6 Y5 Y4 Y3 Y2 Y Y Y5 Y4 Y3 Y2 Y Y Byte 4 X7 X6 X5 X4 X3 X2 X X Byte 5 Y7 Y6 Y5 Y4 Y3 Y2 Y Y * L = Left Key Status M = Middle Key Status R = Right Key Status = Pressed = Released X7-X = X-Axis Movement Data Y7-Y = Y-Axis Movement Data 997 DS59C-page 3

4 The buttons are scanned after a message is sent and the time used to send the message is used as the debouncing time. The message is in an RS-232 format with 2 baud, eight data bits, no parity, and two stop bits. The flowcharts of the main program, subroutine BYTE and subroutine BIT are shown in Figure 5, Figure 6, and Figure 7. Figure 5 shows that the trigger flag is set when any change in button status or X/Y movement is detected. Subroutine BYTE is called in the main program five times to send five bytes of information. Subroutine BYTE controls the status of the Received Data (RD) pin. If Trigger Flag is clear, RD will always be HIGH. Hence, no message will be sent even when subroutine BYTE is called. Figure 7 shows that subroutine BIT counts the number of pulses from the outputs of the photo-transistors, determines the directions, and generates a /2 second delay to get 2 baud timing. The mouse has been tested in Mouse System Mode and functions properly. The setup and software have been tested and function within the given guidlines. A listing of the source program is given in Appendix A. SUMMARY FIGURE 5: FLOWCHART OF THE MAIN PROGRAM Reset Entry Initialize I/O port - Get initial button status Button status change? Set trigger flag X movement count =? Set trigger flag The PIC6C54 from provides a very cost-effective, high performance mouse implementation. Its low power consumption (typically< 2 ma at µs instruction cycle), small package (8-pin) and high reliability (on-chip watchdog timer to prevent software hang-ups) are some of the many reasons why the PIC6C54 is uniquely suitable for mouse applications. Right flag set? Y movement count =? Negate X count te: This application note provides the user with a simple, fully functional serial mouse implementation. The user may use this as a starting point for a more comprehensive design. Set trigger flag Up flag set? Negate Y count Data Button Byte Call Routine BYTE Data X-Coord Byte Call Routine BYTE Data Y-Coord Byte Call Routine BYTE Data X-Coord Byte Call Routine BYTE Data Y-Coor. Byte Call Routine BYTE Set trigger flag DS59C-page 4 997

5 FIGURE 6: FLOWCHART OF ROUTINE BYTE BYTE Count '' TRIGGER flag set? '' RD pin (Start Bit) Call routine BIT TRIGGER flag set? Shift LSb of data to Carry Carry = /? '' RD Pin '' RD pin Call Routine BIT Count Count + Count = 8? Return to Caller 997 DS59C-page 5

6 FIGURE 7: FLOWCHART OF ROUTINE BIT BIT XC = /? XC XC?? X Count X Count + Reset RIGHT Flag X Count X Count + Reset RIGHT Flag XD = /? XD = /? Set RIGHT Flag Set RIGHT Flag YC = /? YC YC?? Y Count Y Count + Reset UP Flag Y Count Y Count + Reset UP Flag YD = /? YD = /? Set UP flag Set TRIGGER flag Delay.833 ms Return to Caller DS59C-page 6 997

7 Please check the Microchip BBS for the latest version of the source code. Microchip s Worldwide Web Address: Bulletin Board Support: MCHIPBBS using CompuServe (CompuServe membership not required). APPENDIX A: MOUSE.ASM MPASM.4 Released MOUSE.ASM :44:22 PAGE LOC OBJECT CODE VALUE LINE SOURCE TEXT TITLE MOUSE 2 LIST P=6C54,R=O 3 ; 4 ; 5 ;******************************************************************** 6 ; 7 ; MOUSE CONTROLLER 8 ; PIC MODE = PIC6C54XT CLK=4.MHZ 9 ; ; Program: MOUSE.ASM ; Revision Date: 25 APRIL, 99 2 ; Compatibility with MPASMWIN.4 3 ; 4 ;******************************************************************** 5 ; 6 ; ; FILES ASSIGNMENT 8 ; ; 3 2 STATUS EQU 3 ;STATUS REGISTER 5 2 RA EQU 5 ;I/O PORT A 6 22 RB EQU 6 ;I/O PORT B 8 23 TIMER EQU ;COUNTER FOR DELAY C 24 CSTAT EQU 4 ;CO-ORDINATE STATUS D 25 BSTAT EQU 5 ;BUTTON STATUS E 26 DATA EQU 6 ; F 27 DATA EQU 7 ; 28 DATA2 EQU 2 ;5 BYTE RS232 DATA 29 DATA3 EQU 2 ; 2 3 DATA4 EQU 22 ; 3 3 FLAGA EQU 23 ;GENERAL PURPOSE FLAG 4 32 XCOUNT EQU 24 ;X-MOVEMENT COUNTER 5 33 YCOUNT EQU 25 ;Y-MOVEMENT COUNTER 6 34 FLAGB EQU 26 ;GENERAL PURPOSE FLAG 8 35 COUNT EQU 3 ;GENERAL PURPOSE COUNTER 9 36 DATA_AREA EQU 3 ;FOR TEMP. STORAGE 37 ; 38 ; ; BIT ASSIGNMENT 4 ; ; 42 YC EQU ;Y-CLOCK PIN 43 YD EQU ;Y-DATA PIN 44 UP EQU ;MOVING UP FLAG 2 45 XC EQU 2 ;X-CLOCK PIN 3 46 XD EQU 3 ;X-DATA PIN 3 47 RI EQU 3 ;MOVING RIGHT FLAG 48 BU EQU ;BUTTON # PIN 2 49 BU2 EQU 2 ;BUTTON #2 PIN 5 CA EQU ;CARRY FLAG 7 5 RD EQU 7 ;RECEIVED DATA PIN TO RS ZERO_AREA EQU 2 ;ZERO FLAG 2 53 TR EQU 2 ;TIGGER FLAG 54 ; 997 DS59C-page 7

8 55 F EQU 56 ; 57 ;=========================================== 58 ; SUBROUTINES 59 ;=========================================== 6 ; 6 ;******************************************* 62 ORG 63 ;******************************************* 64 ; 65 ;=========================================== 66 ; DELAY A BIT TIME AND CHECK XC & YC STATUS 67 ;=========================================== 68 BIT BTFSS RA,XC ;XC =? AA 7 GOTO BIT 2 64C 7 BTFSC CSTAT,XC ;(XC=) 3 A 72 GOTO BITY ;(XC ALWAYS = ) 4 2B4 73 INCF XCOUNT, F ;(XC -- ) BCF FLAGB,RI ;DEFAULT LEFT BTFSS RA,XD ;LEFT / RIGHT? 7 A 76 GOTO BITY BSF FLAGB,RI 9 A 78 GOTO BITY A 79 BIT A 74C 8 BTFSS CSTAT,XC ;(XC=) B A 8 GOTO BITY ;(XC ALWAYS = ) C 2B4 82 INCF XCOUNT, F ;(XC --) D BCF FLAGB,RI ;DEFAULT LEFT E BTFSC RA,XD ;LEFT / RIGHT? F A 85 GOTO BITY BSF FLAGB,RI 87 BITY BTFSS RA,YC ;YC =? 2 AB 89 GOTO BITY 3 6C 9 BTFSC CSTAT,YC ;(YC=) 4 A22 9 GOTO BITDY ;(YC ALWAYS = ) 5 2B5 92 INCF YCOUNT, F ;(YC -- ) BCF FLAGB,UP ;DEFAULT DOWN BTFSS RA,YD ;DOWN / UP? 8 A22 95 GOTO BITDY BSF FLAGB,UP A A22 97 GOTO BITDY B 98 BITY B 7C 99 BTFSS CSTAT,YC ;(YC=) C A22 GOTO BITDY ;(YC ALWAYS = ) D 2B5 INCF YCOUNT, F ;(YC --) E BCF FLAGB,UP ;DEFAULT DOWN F BTFSC RA,YD ;DOWN / UP? 2 A22 4 GOTO BITDY BSF FLAGB,UP 22 6 BITDY MOVF RA,W ;SAVE COOR. STATUS 23 2C 8 MOVWF CSTAT 24 CC 9 MOVLW 93D ;.833 MS DELAY MOVWF TIMER 26 BITD 26 2 NOP 27 2E8 3 DECFSZ TIMER, F 28 A26 4 GOTO BITD RETLW 6 ; 7 ;================================================= 8 ; 9 ;************************************************ 2 ;* SUBROUTINE TO SEND A BYTE * DS59C-page 8 997

9 2 ;* AS RS232C FORMAT 8,N, * 22 ;************************************************ 23 ; 2A 24 BYTE 2A CLRF COUNT ;RESET 8 BIT COUNT 2B BTFSS FLAGA,TR ;ANY TRIGGER 2C A2E 27 GOTO BYTE 2D 4E6 28 BCF RB,RD ;LOW RD FOR START BIT 2E 29 BYTE 2E 9 3 CALL BIT 2F 3 BYTE 2F BTFSS FLAGA,TR ;ANY TRIGGER? 3 A37 33 GOTO BYTE RRF DATA_AREA, F ;SHIFT DATA TO CARRY BTFSS STATUS,CA ; /? 33 A36 36 GOTO BYTE2 34 5E6 37 BSF RB,RD ;SEND A 35 A37 38 GOTO BYTE BYTE2 36 4E6 4 BCF RB,RD ;SEND A 37 4 BYTE CALL BIT 38 2B8 43 INCF COUNT, F BTFSS COUNT,3 ;COUNT = 8? 3A A2F 45 GOTO BYTE 3B BTFSS FLAGA,TR ;ANY TRIGGER? 3C A42 47 GOTO BYTE4 3D 4E6 48 BCF RB,RD ;SEND SENT BIT 3E 9 49 CALL BIT 3F 5E6 5 BSF RB,RD CALL BIT 4 A44 52 GOTO BYTE BYTE CALL BIT CALL BIT BYTE RETLW 58 ; 59 ;============================================ 6 ; RESET ENTRY 6 ;============================================ 62 ; INIT 45 CC 64 MOVLW B ;DISABLE WATCHDOG OPTION 47 CF 66 MOVLW B ;INIT RB~3 BE INPUTS TRIS RB ;RB4~7 BE OUTPUTS 49 CFF 68 MOVLW B ;INIT RA~3 BE INPUTS 4A 5 69 TRIS RA 4B 5E6 7 BSF RB,RD ;HIGH RD PIN 4C COMF RB,W ;GET INIT BUTTON INPUTS 4D E5 72 ANDLW B 4E D8 73 IORLW B 4F 2D 74 MOVWF BSTAT 5 2E 75 MOVWF DATA MOVF RA,W 52 2C 77 MOVWF CSTAT CLRF FLAGA ;CLEAR TR FLAG CLRF XCOUNT ;RESET XCOUNT & YCOUNT CLRF YCOUNT 56 8 SCAN 56 6F 82 CLRF DATA ;UPDATE X,Y MOVEMENT DATA CLRF DATA CLRF DATA CLRF DATA4 5A MOVF XCOUNT,W ;XCOUNT =? 997 DS59C-page 9

10 5B BTFSS STATUS,ZERO_AREA 5C A8 88 GOTO WRITX 5D 89 SCANA 5D 25 9 MOVF YCOUNT,W ;YCOUNT =? 5E BTFSS STATUS,ZERO_AREA 5F A92 92 GOTO WRITY 6 93 SCANB COMF RB,W ;BUTTON STATUS CHANGE? 6 E5 95 ANDLW B 62 D8 96 IORLW B 63 AD 97 SUBWF BSTAT, F BTFSC STATUS,ZERO_AREA ;IF CHANGE THEN TRIGGER 65 A6B 99 GOTO SCANC ;(NO CHANGE) BSF FLAGA,TR ;(CHANGE) SET TRIGGER FLAG COMF RB,W ;FORMAT BUTTON STATUS DATA 68 E5 22 ANDLW B 69 D8 23 IORLW B 6A 2E 24 MOVWF DATA 6B 25 SCANC 6B COMF RB,W 6C E5 27 ANDLW B 6D D8 28 IORLW B 6E 2D 29 MOVWF BSTAT 6F 2E 2 MOVF DATA,W ;SEND DATA,,2,3,4 TO HOST MOVWF DATA_AREA 7 92A 22 CALL BYTE 72 2F 23 MOVF DATA,W MOVWF DATA_AREA 74 92A 25 CALL BYTE MOVF DATA2,W MOVWF DATA_AREA 77 92A 28 CALL BYTE MOVF DATA3,W MOVWF DATA_AREA 7A 92A 22 CALL BYTE 7B MOVF DATA4,W 7C MOVWF DATA_AREA 7D 92A 224 CALL BYTE 7E BCF FLAGA,TR ;CLEAR TRIGGER FLAG 7F A GOTO SCAN 227 ; WRITX BSF FLAGA,TR ;SET TRIGGER FLAG 8 C4 23 MOVLW 4H ;IF XCOUNT > 64 THEN XCOUNT < SUBWF XCOUNT,W BTFSC STATUS,CA 84 A8D 233 GOTO WRITR WRITS BTFSS FLAGB,RI ;LEFT / RIGHT? 86 A9 236 GOTO WRITL COMF XCOUNT, F ;(RIGHT) NEG XCOUNT INCF XCOUNT,W WRITA 89 2F 24 MOVWF DATA 8A 3 24 MOVWF DATA3 8B CLRF XCOUNT ;RESET XCOUNT 8C A5D 243 GOTO SCANA 244 ; 8D 245 WRITR 8D C4 246 MOVLW 4H ;XCOUNT <- 64 8E MOVWF XCOUNT 8F A GOTO WRITS 249 ; 9 25 WRITL MOVF XCOUNT,W ;(LEFT) 9 A GOTO WRITA DS59C-page 997

11 253 ; WRITY BSF FLAGA,TR ;SET TRIGGER FLAG 93 C4 256 MOVLW 4H ;IF YCOUNT > 64 THEN YCOUNT < SUBWF YCOUNT,W BTFSC STATUS,CA 96 A9F 259 GOTO WRITV WRITW BTFSS FLAGB,UP ;DOWN / UP? 98 AA2 262 GOTO WRITD COMF YCOUNT, F ;(UP) NEG YCOUNT 9A INCF YCOUNT,W 9B 265 WRITB 9B MOVWF DATA2 9C MOVWF DATA4 9D CLRF YCOUNT ;RESET YCOUNT 9E A6 269 GOTO SCANB 27 ; 9F 27 WRITV 9F C4 272 MOVLW 4H ;YCOUNT <- 64 A MOVWF YCOUNT A A GOTO WRITW 275 ; A2 276 WRITD A MOVF YCOUNT,W ;(DOWN) A3 A9B 278 GOTO WRITB 279 ; 28 ;=========================================== 28 ; RESET ENTRY 282 ;=========================================== 283 ; FF 284 ORG 777 FF A GOTO INIT ;JUMP TO PROGRAM STARTING 286 ; 287 END : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX 4 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX 8 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXX C : X All other memory blocks unused. Program Memory Words Used: 65 Program Memory Words Free: 347 Errors : Warnings : reported, suppressed Messages : reported, suppressed 997 DS59C-page

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