Advanced C Programming
                                           Spring 2004


Exercise 10. (I/O-ports, CMOS-memory )
         
         Write a program that reads the current date and time from 
         the CMOS memory and displays this data on the screen. In 
         PC:s the information which must be preserved even when the 
         power is switched off are stored in the CMOS memory (setup 
         information). The same IC contains also the RTC (Real Time
         Clock), wich is running when the power is off. The RTC/CMOS
         is a device connected to the bus. It can be accessed via
         i/o-ports. Because RTC/CMOS contains many internal device
         registers (memory locations), the address/data port
         technique (option 3, in the handsout material, part 7) is
         used to keep the number of i/o-ports reasonable. The address
         port is 70H and the dataport is 71H. The layout of the CMOS
         memory (regarding RTC) is decribed below.
    
    
         Remark 1. The setup program which you can start during the
         booting process, reads the information from the CMOS and
         writes it back, when you decide to change setup information. 
     
         Remark 2. The hours, minutes and seconds are stored in
         BCD-format (Binary Coded Decimal). Print the results
         in hexadecimal format (using format specifier %02x) in the
         first version of your program to get the right result. When 
         the results are correct this way, write a function 
         convertBCDtoBin to convert two digit BCD number to binary
         format (two's complement representation). Use this function
         to convert the BCD date, month, year, hours, minutes and
         seconds to binary. After the conversion the result must be
         correct on the screen when you use normal format specifier
         %02d in your printf function. 
       
          
        
         Appendix.

           CMOS address          Contents

              00H                RTC current second
              01H                RTC alarm second 
              02H                RTC current minute
              03H                RTC alarm minute
              04H                RTC current hour
              05H                RTC alarm hour
              06H                RTC current day of the week
              07H                RTC current day of the month
              08H                RTC current month
              09H                RTC current year
              0AH                RTC status register A
              0BH                RTC status register B
              0CH                RTC status register C
              0DH                RTC status register D
              ...                Other information in CMOS memory