AN519. Implementing a Simple Serial Mouse Controller. Implementing a Simple Serial Mouse Controller INTRODUCTION THEORY OF OPERATION

Transcription

1 A59 Implementing a Simple Serial Mouse Controller ITRODUCTIO The mouse is becoming increasingly popular as a standard pointing data entry device. It is no doubt that the demand of the mouse is increasing. Various kinds of mice can be found in the market, including optical mouse, opto-mechanical mouse, and its close relative, trackball. The mouse interfaces to the host via an RS- 3 port or a dedicated interface card. 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, hence 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 Microchip Technology Inc. It is an ideal candidate for a mouse controller. THEOR OF OPERATIO A mouse can be divided into several functional blocks: Microcontroller Button detection Motion detection RS-3 signal generation 5V DC power supply unit A typical functional block diagram is shown in Figure. In Figure, three push buttons 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 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 phototransistor 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 movement is detected, a message is formatted and sent to the host. FIGURE - FUCTIOAL BLOCKS OF A SERIAL MOUSE Quadrature Encoders RS3 PORT OF HOST MICRO- COTROLLER V DC POWER COVERSIO CIRCUITR +5V DC PUSH BUTTOS 993 DS59B-page -7

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 movements. The Microsoft protocol format contains three bytes of data describing the status of two push buttons and the relative X and movements. The details of these protocols are given in Table. Three lines are connected to the host via the RS-3 port: Signal Ground Received Data Request to Send Received Data carries the message sent by the mouse. While Request to Send provides a V DC for voltage conversion circuitry. A voltage of +5V DC is required for electronic components inside the mouse, however, +5V DC is not part of an RS-3 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-3 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 - PIC6C54 PI ASSIGMET +5V DC OSC OSC RB RA RA CLOCK DATA SIGALS FROM -COORD. PHOTO-TRASISTOR RB RB RA RA3 XCLOCK XDATA SIGALS FROM X-COORD. PHOTO-TRASISTOR VDD MCLR RB7 GD RECEIVED DATA PI OF HOST RS3 PORT FIGURE 3 - VOLTAGE COVERSIO CIRCUITR RS3 PORT RTS SIGAL GD RESET VCC OUTPUT DISCHARGE 555 THRESHOLD TRIGGER 33 µf.5 µf K K -V to V V to +V µf 5 K +5V DC OUTPUT DS59B-page

3 ABOUT THE SOFTWARE The major tasks performed by the software are button scanning, X and 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- 3 port. The number of pulses reflects the speed of the movement. The more number of pulses, the faster the movement is. The directions of the 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 FIGURE 4 - VOLTAGE COVERSIO CIRCUITR 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 is positive, it indicates that the mouse is moving down and if 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 / second to send, if the distance between the grid lines is mm, the tracking speed will be up to mm/second. XCLOCK (XC) XDATA (XD) MOVE RIGHT MOVE LEFT CLOCK (C) DATA (D) MOVE UP MOVE DOW TABLE - MOUSE SSTEM AD MICROSOFT PROTOCOLS Mouse System Format* Microsoft Format* Bit Position Byte L M R L R 7 6 X7 X6 Byte X7 X6 X5 X4 X3 X X X X5 X4 X3 X X X Byte Byte 4 X7 X6 X5 X4 X3 X X X Byte * L = Left Key Status M = Middle Key Status R = Right Key Status = Pressed = Released X7-X = X-Axis Movement Data 7- = -Axis Movement Data 993 DS59B-page 3-73

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-3 format with baud, eight data bits, no parity, and two stop bits. The flow charts of the main program, subroutine BTE and subroutine BIT are shown in Figures 5, 6, and 7. Figure 5 shows the Trigger Flag is set when any change of button status or X/ movement is detected. Subroutine BTE is called in the main program five times to send five bytes of information. Subroutine BTE 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 BTE is called. Figure 7 shows that subroutine BIT counts the number of pulses from outputs of the photo-transistors, determines the directions, and generates / second delay to get baud timing. The mouse has been tested in Mouse System Mode and is functioning properly. A completed listing of the source program is given in Appendix A. SUMMAR The PIC6C54 from provides a very cost-effective, high performance mouse implementation. Its low power (typically < ma at µs instruction cycle), small package (8-pin) and high reliability (on-chip watchdog timer to prevent software hangups) are among several reasons why the PIC6C54 is uniquely suitable for mouse applications. FIGURE 5 - FLOW CHART OF THE MAI PROGRAM Reset Entry Initialize I/O Port - Get Initial Button Status Button Status Change Set Trigger Flag X Movement Count = Set Trigger Flag Right Flag Set egate X Count 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. For fully implemented and compliant mouse products see Microchip's ASSP device family (MTA4XXX). Movement Count = Set Trigger Flag Up Flag Set egate Count Data Button Byte Call Routine Byte Data X-Coor. Byte Call Routine Byte Data -Coor. Byte Call Routine Byte Data X-Coor. Byte Call Routine Byte Data -Coor. Byte Call Routine Byte Set Trigger Flag DS59B-page

5 FIGURE 6 - FLOW CHART OF ROUTIE BTE 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 993 DS59B-page 5-75

6 FIGURE 7 - FLOW CHART OF ROUTIE 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 C = / C C Count Count + Reset Up Flag Count Count + Reset Up Flag D = / D = / Set Up Flag Set Trigger Flag Delay.833 ms Return to Caller DS59B-page

7 APPEDIX A: MPASM B.54 PAGE MOUSE TITLE MOUSE LIST P=6C54,R=O ******************************************* * * * MOUSE COTROLLER * * * * VERSIO : 5 APRIL, 99 * * * * MODE = PIC6C54XT CLK=4.MHZ * ******************************************* FILES ASSIGMET 3 STATUS EQU 3 STATUS REGISTER 5 RA EQU 5 I/O PORT A 6 RB EQU 6 I/O PORT B 8 TIMER EQU COUTER FOR DELA C CSTAT EQU 4 CO-ORDIATE STATUS D BSTAT EQU 5 BUTTO STATUS E DATA EQU 6 F DATA EQU 7 DATA EQU 5 BTE RS3 DATA DATA3 EQU DATA4 EQU 3 FLAGA EQU 3 GEERAL PURPOSE FLAG 4 XCOUT EQU 4 X-MOVEMET COUTER 5 COUT EQU 5 -MOVEMET COUTER 6 FLAGB EQU 6 GEERAL PURPOSE FLAG 8 COUT EQU 3 GEERAL PURPOSE COUTER 9 DATA_AREA EQU 3 FOR TEMP. STORAGE BIT ASSIGMET C EQU -CLOCK PI D EQU -DATA PI UP EQU MOVIG UP FLAG XC EQU X-CLOCK PI 3 XD EQU 3 X-DATA PI 3 RI EQU 3 MOVIG RIGHT FLAG BU EQU BUTTO # PI BU EQU BUTTO # PI CA EQU CARR FLAG 7 RD EQU 7 RECEIVED DATA PI TO RS3 ZERO_AREA EQU ZERO FLAG TR EQU TIGGER FLAG =========================================== SUBROUTIES =========================================== ******************************************* ORG ******************************************* =========================================== DELA A BIT TIME AD CHECK XC & C STATUS =========================================== 993 DS59B-page 7-77

8 BIT 745 BTFSS RA,XC XC = AA GOTO BIT 64C BTFSC CSTAT,XC (XC=) 3 A GOTO BIT (XC ALWAS = ) 4 B4 ICF XCOUT (XC ) BCF FLAGB,RI DEFAULT LEFT BTFSS RA,XD LEFT / RIGHT 7 A GOTO BIT BSF FLAGB,RI 9 A GOTO BIT BIT A 74C BTFSS CSTAT,XC (XC=) B A GOTO BIT (XC ALWAS = ) C B4 ICF XCOUT (XC ) D 476 BCF FLAGB,RI DEFAULT LEFT E 665 BTFSC RA,XD LEFT / RIGHT F A GOTO BIT 576 BSF FLAGB,RI BIT 75 BTFSS RA,C C = AB GOTO BIT 3 6C BTFSC CSTAT,C (C=) 4 A GOTO BITD (C ALWAS = ) 5 B5 ICF COUT (C ) BCF FLAGB,UP DEFAULT DOW 7 75 BTFSS RA,D DOW / UP 8 A GOTO BITD BSF FLAGB,UP A A GOTO BITD BIT B 7C BTFSS CSTAT,C (C=) C A GOTO BITD (C ALWAS = ) D B5 ICF COUT (C ) E 436 BCF FLAGB,UP DEFAULT DOW F 65 BTFSC RA,D DOW / UP A GOTO BITD 536 BSF FLAGB,UP BITD 5 MOVF RA,W SAVE COOR. STATUS 3 C MOVWF CSTAT 4 CC MOVLW 93D.833 MS DELA 5 8 MOVWF TIMER BITD 6 OP 7 E8 DECFSZ TIMER 8 A6 GOTO BITD 9 8 RETLW ================================================= ************************************************ * SUBROUTIE TO SED A BTE * * AS RS3C FORMAT 8,, * ************************************************ BTE A 78 CLRF COUT RESET 8 BIT COUT B 753 BTFSS FLAGA,TR A TRIGGER C AE GOTO BTE D 4E6 BCF RB,RD LOW RD FOR START BIT BTE E 9 CALL BIT BTE F 753 BTFSS FLAGA,TR A TRIGGER 3 A37 GOTO BTE RRF DATA_AREA SHIFT DATA TO CARR 3 73 BTFSS STATUS,CA / 33 A36 GOTO BTE DS59B-page

9 34 5E6 BSF RB,RD SED A 35 A37 GOTO BTE3 BTE 36 4E6 BCF RB,RD SED A BTE CALL BIT 38 B8 ICF COUT BTFSS COUT,3 COUT = 8 3A AF GOTO BTE 3B 753 BTFSS FLAGA,TR A TRIGGER 3C A4 GOTO BTE4 3D 4E6 BCF RB,RD SED SET BIT 3E 9 CALL BIT 3F 5E6 BSF RB,RD 4 9 CALL BIT 4 A44 GOTO BTE5 BTE4 4 9 CALL BIT 43 9 CALL BIT BTE RETLW ============================================ RESET ETR ============================================ IIT 45 CC MOVLW B ' DISABLE WATCH DOG 46 OPTIO 47 CF MOVLW B ' IIT RB~3 BE IPUTS 48 6 TRIS RB RB4~7 BE OUTPUTS 49 CFF MOVLW B ' IIT RA~3 BE IPUTS 4A 5 TRIS RA 4B 5E6 BSF RB,RD HIGH RD PI 4C 46 COMF RB,W GET IIT BUTTO IPUTS 4D E5 ADLW B ' 4E D8 IORLW B ' 4F D MOVWF BSTAT 5 E MOVWF DATA 5 5 MOVF RA,W 5 C MOVWF CSTAT CLRF FLAGA CLEAR TR FLAG CLRF XCOUT RESET XCOUT & COUT CLRF COUT SCA 56 6F CLRF DATA UPDATE X, MOVEMET DATA 57 7 CLRF DATA 58 7 CLRF DATA CLRF DATA4 5A 4 MOVF XCOUT,W XCOUT = 5B 743 BTFSS STATUS,ZERO_AREA 5C A8 GOTO WRITX SCAA 5D 5 MOVF COUT,W COUT = 5E 743 BTFSS STATUS,ZERO_AREA 5F A9 GOTO WRIT SCAB 6 46 COMF RB,W BUTTO STATUS CHAGE 6 E5 ADLW B ' 6 D8 IORLW B ' 63 AD SUBWF BSTAT BTFSC STATUS,ZERO_AREA IF CHAGE THE TRIGGER 65 A6B GOTO SCAC (O CHAGE) BSF FLAGA,TR (CHAGE) SET TRIGGER FLAG COMF RB,W FORMAT BUTTO STATUS DATA 68 E5 ADLW B ' 69 D8 IORLW B ' 993 DS59B-page 9-79

10 6A E MOVWF DATA SCAC 6B 46 COMF RB,W 6C E5 ADLW B ' 6D D8 IORLW B ' 6E D MOVWF BSTAT 6F E MOVF DATA,W SED DATA,,,3,4 TO HOST 7 39 MOVWF DATA_AREA 7 9A CALL BTE 7 F MOVF DATA,W MOVWF DATA_AREA 74 9A CALL BTE 75 MOVF DATA,W MOVWF DATA_AREA 77 9A CALL BTE 78 MOVF DATA3,W MOVWF DATA_AREA 7A 9A CALL BTE 7B MOVF DATA4,W 7C 39 MOVWF DATA_AREA 7D 9A CALL BTE 7E 453 BCF FLAGA,TR CLEAR TRIGGER FLAG 7F A56 GOTO SCA WRITX BSF FLAGA,TR SET TRIGGER FLAG 8 C4 MOVLW 4H IF XCOUT > 64 THE XCOUT < SUBWF XCOUT,W BTFSC STATUS,CA 84 A8D GOTO WRITR WRITS BTFSS FLAGB,RI LEFT / RIGHT 86 A9 GOTO WRITL COMF XCOUT (RIGHT) EG XCOUT ICF XCOUT,W WRITA 89 F MOVWF DATA 8A 3 MOVWF DATA3 8B 74 CLRF XCOUT RESET XCOUT 8C A5D GOTO SCAA WRITR 8D C4 MOVLW 4H XCOUT <- 64 8E 34 MOVWF XCOUT 8F A85 GOTO WRITS WRITL 9 4 MOVF XCOUT,W (LEFT) 9 A89 GOTO WRITA WRIT BSF FLAGA,TR SET TRIGGER FLAG 93 C4 MOVLW 4H IF COUT > 64 THE COUT < SUBWF COUT,W BTFSC STATUS,CA 96 A9F GOTO WRITV WRITW BTFSS FLAGB,UP DOW / UP 98 AA GOTO WRITD COMF COUT (UP) EG COUT 9A 95 ICF COUT,W WRITB 9B 3 MOVWF DATA 9C 3 MOVWF DATA4 9D 75 CLRF COUT RESET COUT 9E A6 GOTO SCAB DS59B-page

11 WRITV 9F C4 MOVLW 4H COUT <- 64 A 35 MOVWF COUT A A97 GOTO WRITW WRITD A 5 MOVF COUT,W (DOW) A3 A9B GOTO WRITB =========================================== RESET ETR =========================================== ORG 777 FF A45 GOTO IIT JUMP TO PROGRAM STARTIG ED ******************************************** Errors : Warnings : 993 DS59B-page -8

12 OTES: DS59B-page

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