AN INTRODUCTION TO SERIAL PORT INTERFACING - www.onlineTPS.com

1. AN INTRODUCTION TO SERIAL PORT INTERFACING

7. Advantage of Start / Stop bits

9. Overview of total bits with Parity Odd Parity Odd parity is added to keep the no. of 1’s odd in transmission. For example for above case of data being 10011101 The odd parity will be added as 0 as no of 1’s are already 5 (an odd no.).

12. Serial / RS-232 Port on PC & its Pin Out

15. Configuration of Serial Port Base Address DLAB Read/ Write Abr. Registered Mar-- +0 0 0 1 W R R/W - - - Transmit holding buffer Receive Buffer Divisor latch low byte +1 0 1 R/W R/W IER Interrupt enable register Divisor latch high byte +2 - - R W IIR FCR Interrupt Identification Register FIFO Control register. +3 +4 +5 +6 +7 - - - - - R/W R/W R R R/W LCR MCR LSR MSR - Line Control Register modem Control Register Line Status Register Modem Status Register Scratch Register.

19. Bit # Functional Description 7 1 Divisor Latch Access Bit ( DLAB ON ) 0 DLAB=0, Access to Tx/Rx & IER for normal operation 6 Set Brake Enable 3:5 Bit 5 Bit 4 Bit 3 Parity Select x x 0 No Parity 0 0 1 1 0 1 0 1 1 1 1 1 Odd Parity Even Parity High Parity ( Sticky ) Low Parity ( Sticky ) 2 Length of stop bit 0 One stop bit 1 2 stop bits for words of length 6, 7 or 8 bits 1.5 stop bits for words of length 5 bits 0:1 Bit 1 Bit 0 Word Length 0 0 1 1 0 1 0 1 5 Bits 6 Bits 7 Bits 8 Bits

20. The Function of various pins on Serial Port Pin # on DB – 9 Pin Symbol Function 1 CD Carrier Detect: It is used by Modem to inform PC that it has detected Carrier on Phone Line. 2 RD Serial data is received on this line by PC. 3 TD Serial Data is transmitted on this pin by PC. 4 DTR Data Terminal Ready When terminal (computer) powers up it asserts DTR high. 5 SG It is signal ground with reference to which voltages are interpreted as high or low. 6 DSR Data Set Ready. When modem powers up it asserts DSR high. 7 RTS Request to Send. Request to send is sent from (DTE) terminal (PC) to modem (DCE) to inform it that PC wants to send some data to modem.

21. The Function of various pins on Serial Port (Contd) 8 CTS Clear To Send. Upon received RTS from DTE (PC), the modem (DCE) asserts CTS high whenever it is ready to receive data. 9 RI Ring Indicator. It is set by modem to indicate the PC that a ringing signal has been detected on line.

31. USB implementation model