一个基于单片机IO的键盘扫描函数

				### uVision2 Project, (C) Keil Software
				### Do not modify !
				
				Target (Target 1), 0x0000 // Tools: 'MCS-51'
				
				Group (Source Group 1)
				
				File 1,1,
				
				
				Options 1,0,0  // Target 'Target 1'
				 Device (AT89S52)
				 Vendor (Atmel)
				 Cpu (IRAM(0-0xFF) IROM(0-0x1FFF) CLOCK(33000000) MODAT2)
				 FlashUt ()
				 StupF ("LIB\STARTUP.A51" ("Standard 8051 Startup Code"))
				 FlashDR ()
				 DevID (3411)
				 Rgf (REGX51.H)
				 Mem ()
				 C ()
				 A ()
				 RL ()
				 OH ()
				 DBC_IFX ()
				 DBC_CMS ()
				 DBC_AMS ()
				 DBC_LMS ()
				 UseEnv=0
				 EnvBin ()
				 EnvInc ()
				 EnvLib ()
				 EnvReg (