\nThe joystick buttons on the TRS-80 Color Computer 1 (CoCo 1) are connected to the\nPIA (Peripheral Interface Adapter). They can be read from memory location\n \nIn Color BASIC, the value can be read using \nThe joystick buttons are active low<\/strong>. This means that a button that\nis not pressed reads as a \nThe button bits are:\n<\/p>\n \nColor BASIC supports bitwise \nThe parentheses are important. Color BASIC’s operator precedence can produce\nsurprising results if you write:\n<\/p>\n \nThis is not interpreted as:\n<\/p>\n \nInstead, the comparison happens first, effectively making it:\n<\/p>\n \nSince \nThe correct way to test a bit is to put the bit operation inside parentheses:\n<\/p>\n \nThe evaluation order is:\n<\/p>\n \nThis is a good habit for Color BASIC programming: whenever using bit masks in\na comparison, put the masked expression in parentheses.\n<\/p>\n \nThe CoCo’s joystick interface is simple, but remembering that the buttons are\nactive low and that Color BASIC’s operator precedence is different from many\nmodern languages will save a lot of debugging time.\n<\/p>","protected":false},"excerpt":{"rendered":" Reading CoCo Joystick Buttons in Color BASIC The joystick buttons on the TRS-80 Color Computer 1 (CoCo 1) are connected to the PIA (Peripheral Interface Adapter). They can be read from memory location $FF00, which is decimal 65280. In Color … Continue reading $FF00<\/code>, which is decimal 65280<\/code>.\n<\/p>\nPEEK<\/code>:\n<\/p>\nB=PEEK(65280)<\/code><\/pre>\n1<\/code>, and a pressed button pulls the bit to\n<\/code>.\n<\/p>\n\n
\n Bit<\/th>\n Mask<\/th>\n Button<\/th>\n<\/tr>\n \n 0<\/td>\n 1<\/code><\/td>\nRight joystick button<\/td>\n<\/tr>\n \n 1<\/td>\n 2<\/code><\/td>\nLeft joystick button<\/td>\n<\/tr>\n<\/table>\n AND<\/code>, which makes checking the buttons\nstraightforward:\n<\/p>\n10 B=PEEK(65280)\n20 IF (B AND 1)=0 THEN PRINT "RIGHT BUTTON"\n30 IF (B AND 2)=0 THEN PRINT "LEFT BUTTON"\n40 GOTO 10<\/code><\/pre>\nPEEK(65280) AND 128 = 0<\/code><\/pre>\n(PEEK(65280) AND 128) = 0<\/code><\/pre>\nPEEK(65280) AND (128 = 0)<\/code><\/pre>\n128 = 0<\/code> is false, the expression becomes an AND with zero,\nwhich will always produce zero.\n<\/p>\n(PEEK(65280) AND 128) = 0<\/code><\/pre>\n\n
PEEK(65280)<\/code> reads the hardware register.<\/li>\nAND 128<\/code> masks the desired bit.<\/li>\n= 0<\/code> tests whether that bit is clear.<\/li>\n<\/ol>\n