#include processor p16f630 ; Sega Mega Drive/Genesis switchless mod ; d4s 2010-10-31 matt@dforce3000.de ; ; Pressing Mega Drive reset switch cycles through three available modes indicated by Status LED color: ; -50Hz/en (Europe, green) ; -60Hz/en (USA, orange) ; -60Hz/jp (Japan, red) ; ; Both active-high and active-low reset consoles are supported by sensing the reset line level ; on startup. ; Indicator LED is optional, but strongly recommended. ; See corresponding PDF file for connection points on different pcb versions ; ; Tested working on the following pcb versions: ; -IC BD M5 PAL VA4 (PAL early Mega Drive Mk1, active-high reset) ; -IC BD M5 PAL (PAL late Mega Drive Mk1, active-low reset) ; -PC BD MD2 VA1.8 PAL (PAL Mega Drive Mk2, active-low reset) ; ; Untested on american, japanese or Mk3 consoles, but should work in theory. ; Please report your experience with any pcb versions not listed here. ; ; pin configuration: ; ; ,-----_-----. ; +5V |1 14| GND ; |2 A5 A0 13| RESET_IN, /RESET_IN (Reset Button) ; |3 A4 A1 12| ; |4 A3 A2 11| ; (red) LED_OUT2 |5 C5 C0 10| LANGUAGE_OUT (en/jp) ; (grn) LED_OUT1 |6 C4 C1 9| VIDEOMODE_OUT (50/60Hz) ; |7 C3 C2 8| RESET_OUT, /RESET_OUT (VDP reset line) ; `-----------' ; ; (/)RESET_IN - Reset Button Input (needs pulldown resistor (5 KOhm) on active-high reset consoles). * ; LANGUAGE_OUT - English(high)/Japanese(low), JP1/JP2 on Mega Drive Mk1, C65/C68 on Genesis 3. ** ; VIDEOMODE_OUT - 60Hz(high)/50Hz(low), JP3/JP4 on Mega Drive Mk1, C63/C64 on Genesis 3. ** ; (/)RESET_OUT - Reset output to videochip. * : LED_OUT1, LED_OUT2 - Use 3-pin dual-color (red/green) LED here. Connect common base of LED to GND via 220 Ohm resistor. ; ; * Cut reset line between reset button and videochip. Be sure to leave pulldown resistor connected to reset button on active-high reset units. ; ** Make sure to remove/cut any connection on set jumpers. Mk2 consoles don't have any jumpers, you'll have to cut lines here. ; ; If you experience noise problems, you may add a capacitor near the PIC between the +5V and GND lines. I never had any, though. ; ; Parts needed: ; -Microchip PIC 16f630 ; -Some wire ; -Dual-color LED (optional) ; -220 Ohm resistor (optional) ; -100nF Ceramic Capacitor (optional) ; ; ----------------------------------------------------------------------- __CONFIG _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF ;port a RESET_BUTTON equ 0 ;port c LANGUAGE equ 0 VIDEOMODE equ 1 RESET_OUT equ 2 LED1 equ 4 LED2 equ 5 ;bitflags for byte ops RESET_BUTTON_BIT equ 1 << RESET_BUTTON LED1_BIT equ 1 << LED1 LED2_BIT equ 1 << LED2 LANGUAGE_BIT equ 1 << LANGUAGE RESET_OUT_BIT equ 1 << RESET_OUT VIDEOMODE_BIT equ 1 << VIDEOMODE ;variables varBlock udata_shr modeCounter res 1 outBuffer res 1 waitBuff res 2 buttonStatus res 1 buff res 1 resetInversion res 1 ;code start boot code 0 goto main main call init call senseResetInversion call clearReset call loadModeFromEEPROM call setLEDs call applySettings mainLoop call getResetButtonState btfss buttonStatus,1 ;wait for press on reset button goto mainLoop call waitLong call getResetButtonState btfsc buttonStatus,1 ;if release occured, reset console goto changeSettingsLoop call doReset goto mainLoop changeSettingsLoop call cycleModeCounter call setLEDs call waitLong call getResetButtonState btfsc buttonStatus,1 ;cycle modes while reset button is held down goto changeSettingsLoop call applySettings ;set mode and save to EEPROM if button released call saveModeToEEPROM goto mainLoop applySettings movfw PORTC movwf outBuffer bcf outBuffer, LANGUAGE bcf outBuffer, VIDEOMODE btfsc modeCounter, 0 bsf outBuffer, LANGUAGE btfsc modeCounter, 1 bsf outBuffer, VIDEOMODE movfw outBuffer movwf PORTC return setLEDs movfw PORTC movwf outBuffer bcf outBuffer, LED1 bcf outBuffer, LED2 btfsc modeCounter, 0 bsf outBuffer, LED1 btfsc modeCounter, 1 bsf outBuffer, LED2 movfw outBuffer movwf PORTC return clearLEDs bcf PORTC, LED1 bcf PORTC, LED2 return loadModeFromEEPROM banksel EEADR ;fetch current mode from EEPROM clrf EEADR ;address 0 bsf EECON1, RD movfw EEDAT banksel PORTA andlw 3 ;compensate for invalid modes(initial run or bad EEPROM) btfsc STATUS,Z movlw 1 movwf modeCounter return saveModeToEEPROM movfw modeCounter banksel EEADR ;save to EEPROM. note: banksels take two cycles each! movwf EEDAT bsf EECON1,WREN movlw 0x55 movwf EECON2 movlw 0xaa movwf EECON2 bsf EECON1, WR banksel PORTA return cycleModeCounter decfsz modeCounter goto dontResetModeCount movlw 3 ;mode counter underflowed, reset to maximum movwf modeCounter dontResetModeCount movfw modeCounter ;clip to maximum of 3 modes(+1 underflow detect) andlw 3 movwf modeCounter return getResetButtonState clrf buttonStatus call getResetInvertedPort btfss buff, RESET_BUTTON return call wait ;debounce reset button call getResetInvertedPort btfss buff, RESET_BUTTON return bsf buttonStatus,1 return senseResetInversion clrf resetInversion ;invert reset in/out depending on initial reset line state btfsc PORTA, RESET_BUTTON bsf resetInversion, 1 return getResetInvertedPort movfw PORTA btfsc resetInversion, 1 xorlw RESET_BUTTON_BIT movwf buff return doReset call setReset call waitLong call clearReset return setReset btfsc resetInversion, 1 goto setLowReset goto setHighReset clearReset btfsc resetInversion, 1 goto setHighReset goto setLowReset setHighReset bsf PORTC, RESET_OUT return setLowReset bcf PORTC, RESET_OUT return init bcf STATUS, RP0 ;bank 0 regs clrf PORTA ;clear ports clrf PORTC movlw 0x07 ;a0/a2 digital movwf CMCON clrf INTCON ;disable all interrupts, disable port a pullups bsf STATUS, RP0 ;bank 1 regs clrf TRISA bsf TRISA, RESET_BUTTON clrf TRISC movlw 0b111111 ;maximum frequency movwf OSCCAL clrf WPUA bsf WPUA, RESET_BUTTON ;weak pullup on reset button clrf OPTION_REG bcf OPTION_REG, NOT_RAPU ;enable pullups on port a bcf STATUS, RP0 ;return to bank 0 bcf INTCON, RAIF ;clear irq on change flag return waitLong clrf waitBuff+1 waitLongLoop call wait decfsz waitBuff+1, f goto waitLongLoop return wait clrf waitBuff waitLoop nop nop nop nop nop nop nop nop decfsz waitBuff, f goto waitLoop return end