请教CCD程序

joicejoy

  //初始化PIT
  PITCFLMT = 0x80;//Enable PIT
  PITCE = 0x03;//Enable channel 0,1
  PITMUX = 0x00;
  PITINTE = 0x03;//Enable the interrupt of channel 0,1
  
  PITMTLD0 = 199;
  PITLD0 = 1999;//PIT0 is 100Hz
  PITLD1 = 199;//改这个值控制曝光时间，值越大曝光时间越短
  
  DDRB = 0xFF;
  DDRS = 0xFF;
  DDRA = 0x00;
  DDRE = 0xFF;
  DDRT = 0x03;  //PT0 & PT1 are output
  //PT1:SI  PT0:CLK


PITLD1 = 199;//改这个值怎么控制曝光时间啊？