1. Lecture 15

2. Modem Controller Register 4310 DTR 0 = Polling Operator 1 = Interrupts Enabled RTS 1 =Self Test 0 =Normal

3. Modem Status Register 76543210 CD Change in CTS Change in RI Change in CD CTS RI DSR Change in DSR

4. UART (16550) FIFO QUEUE 76210 FIFO buffer on=1 Clear send Buffer =1 Number of Characters Received To Trigger an Interrupt 00 =After Every Character 01 =After 4 Character 10 =After 8 Character 11 =After 14 Character Clear Receiver Buffer =1

5. Interrupt ID Register (Revisited) 763210 Interrupt Triggered =1 Any one of these BEING Set Indicates FIFO is ON. Reasons of Interrupt 00= Change in Modem Line Status 01=THR is Empty 10=Data is ready 11=Error in Data Transmit 1= Interrupt Triggered Because Buffer is not full But other side has stop sending data. (Time OUT)

6. BIOS support for COM ports: INT# 14H DX = port # 0 for COM1 1 for COM2 etc. Service# 0 = Set communication parameters Service# 01 = Output character Service# 02 = Read in characters Service# 03 = Get port status

7. Data Length 00 = 5bits 01 = 6bits 10 = 7bits 11 = 8bits # of stop bits 0 = 1 stop bit 1 = 1.5 or 2 stop bit Parity Check 00 = None 01 = Odd 10 = Parity Disable 11 = Even Baud Rate 000 = 110 bauds 001 = 150 bauds 010 = 300 bauds 011 = 600 bauds 100 = 1200 bauds 101 = 2400 bauds 110 = 4800 bauds 111 = 9600 bauds Service # 0 AL =

8. Data Ready Over run error Parity error Framing error Time Out TSR Empty THR Break Detected AH = Line Status

9. Change in CTS Change in DSR Change in RI Change in CD CD RI Ready (DSR) Ready to Receive AL = Modem Status

10. Service # 01 ON ENTRY AL = ASCII character to send ON RETURN AH = Error Code If 7 th bit in AH = 1 = Unsuccessful 0 = Successful Service # 02 ON RETURN AL = ASCII character received AH = Error Code

11. Modem PC Modem UARTDigital DataAnalog Tel Line UART PC Modem Digital DataAnalog

12. NULL Modem PC Cable UART

13. 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 DTR DSR RTS CTS DSR DTR CTS RTS

14. Example: #include char ch1, ch2; void initialize (int pno) { _AH=0; _AL=0x57; _DX=pno; geninterrupt(0x14); }

15. char receivechar (int pno) { char ch; _DX = pno; _AH = 2; geninterrupt (0x14); ch = _AL; return ch; }

16. void sendchar (char ch, int pno) { _DX = pno; _AH = 1; _AL = ch; geninterrupt (0x14); } unsigned int getcomstatus (int pno) { unsigned int temp; _DX = pno; _AH = 03; geninterrupt (0x14); *((char*)(&temp)) = _AL; *(((char*)(&temp)) + 1) = _AH; return temp; }