1. Lecture 17

2. #include <dos. h> #include <bios
#include <dos.h> #include <bios.h> char ch1,ch2; void initialize (unsigned int com) { outportb ( com+3, inport (com+3) | 0x80); outportb ( com,0x80); outportb( com +1, 0x01); outportb ( com+3, 0x1b); }

3. void main ( ) {. initialize(0x3f8);. while (1). {
void main ( ) { initialize(0x3f8); while (1) { if ( ((inport(0x3fd)&0x20)==0x20) && (kbhit())) { ch1=getche(); outport(0x3f8,ch1); } if (( (inport(0x3fd)&0x01)==1)) { ch2= inport(0x3f8); putch(ch2); } if (( ch1==27) || (ch2==27)) break; } }

4. NULL Modem (Revisited)
CD 1
RxD 2
TxD 3
DTR 4
GND 5
DSR 6
RTS 7
CTS 8
RI 9
CD 1
RxD 2
TxD 3
DTR 4
GND 5
DSR 6
RTS 7
CTS 8
RI 9

5. NULL Modem (Revisited)
CD 1
RxD 2
TxD 3
DTR 4
GND 5
DSR 6
RTS 7
CTS 8
RI 9
CD 1
RxD 2
TxD 3
DTR 4
GND 5
DSR 6
RTS 7
CTS 8
RI 9

6. Software Oriented Flow Control Makes use of Two Control characters.
XON (^S)
XOFF (^T)

7. while (1) {. receivedchar = readchar (com);. if (receivedchar == XON)
while (1) { receivedchar = readchar (com); if (receivedchar == XON) { ReadStatus = TRUE; continue; } if (receivedchar == XOFF) { ReadStatus = FALSE; continue; } if (ReadStatus == TRUE) Buf [i++] = receivedchar; }

8. Time Updation Through INT8
Real Time Clock Device
Battery powered device
Updates time even if PC is shutdown
RTC has 64 byte battery powered RAM
INT 1AH used to get/set time.

9. Clock Counter 1AH/00 (hours*60*60 + min*60 + sec) * 18.2065
ON ENTRY
AH = 00
ON EXIT
AL = Midnight flag
CX = Clock count (Hi word)
DX = Clock count (Low word)
Times Increment
/ = sec
Whereas sec represent 24 hrs.

10. AL = 1 if Midnight passed AL = 0 if Midnight not passed Set Clock Counter 1AH/01
ON ENTRY
AH = 01
CX = Clock count (Hi word)
DX = Clock count (Low word)

11. Read Time 1AH/02 ON ENTRY AH = 02 ON EXIT CH = Hours (BCD)
CL = Minutes (BCD)
DH = Seconds (BCD)

12. Set Time 1AH/03 ON ENTRY AH = 03 CH = Hours (BCD) CL = Minutes (BCD)
DH = Seconds (BCD)
DL = Day Light saving = 1
Standard Time = 0

13. Read Date 1AH/04 ON ENTRY AH = 04 ON EXIT CH = Century (BCD)
CL = Year (BCD)
DH = Month (BCD)
DL = Day (BCD)

14. Set Date 1AH/05 ON ENTRY AH = 05 CH = Century (BCD) CL = Year (BCD)
DH = Month (BCD)
DL = Day (BCD)

15. Set Alarm 1AH/06 ON ENTRY AH = 06 CH = Hours (BCD) CL = Minutes (BCD)
DH = Seconds (BCD)

16. Disable Alarm 1AH/07
ON ENTRY
AH = 07

17. Read Alarm 1AH/09 ON ENTRY AH = 09 ON EXIT CH = Hours (BCD)
CL = Minutes (BCD)
DH = Seconds (BCD)
DL = Alarm Status (00 = Not Enable
01 = Enable)

18. Real Time Clock Control Circuitry
Clock and Logic circuitry
64 Bytes Battery Powered Low power CMOS RAM
70H
Control Circuitry
71H
::::::::::::::::::::::::::::::::::::
INT
7FH

19. Internal Ports 70 – 7FH (16 ports)
Only 70 & 71H are important from programming point of view

20. 64 Byte Battery Powered RAM
00H = Current Second
01H = Alarm Second
02H = Current Minute
03H = Alarm Minute
04H = Current Hour
05H = Alarm Hour
06H = Day Of the Week
07H = Number Of Day

21. 64 Byte Battery Powered RAM
08H = Month
09H = Year
0AH = Clock Status Register A
0BH = Clock Status Register B
0CH = Clock Status Register C
0DH = Clock Status Register D
32H = Century

22. Week Day 01H = Sunday 02H = Monday 03H = Tuesday 04H = Wednesday
05H = Thursday
06H = Friday
07H = Saturday

23. Year
No of Century and Year are in BCD.

24. Accessing the Battery Powered RAM
Battery Powered RAM is accessed in two steps
Specify the Byte no. in 70H port.
Read/write port 71H to get/set the value of specified byte.

25. Accessing the Battery Powered RAM
outport (0x70, 0); outport (0x70, 4);
sec = inport (0x71); outport (0x71,hrs);

26. Status Register A 7 6 5 4 3 2 1 0 Interrupt frequency Time frequency
Interrupt frequency
Time frequency
0 = Time is not updated
1 = Time is updated