RS 232 Serial Communication Standards

By -

8.4 RS 232 Serial Communication Standards

In serial I/O, data can be transmitted as either current or voltage. When data is transmitted as voltage, the commonly used standard is known as RS-232C. This standard was developed by Electronic Industries Association (EIA), USA and adopted by IEEE. RS-232 standard proposes a maximum of 25 signals for the bus used for serial data transfer.

8.4.1 RS-232 Pin Names and Signal Descriptions

Pin Number

Common Name

RS-232 Name

Description

1

-

AA

Protective Ground

2

TxD

BA

Transmitted Data

3

RxD

BB

Received Data

4

RTS

CA

Request to Send

5

CTS

CB

Clear to Send

6

DSR

CC

Data Set Ready

7

GND

AB

Signal Ground

8

CD

CF

Received Line signal detector

9

-

-

Reserved for Data set testing

10

-

-

Reserved for Data set testing

12

-

SCF

Secondary Receiver Line Signal Detector

13

-

SCB

Secondary Clear to Send

14

-

SBA

Secondary Transmitted Data

15

-

DB

Transmission signal element timing

16

-

SBF

Secondary Received Data

17

-

DD

Receiver Signal element timing

18

-

-

Unassigned

19

-

SCA

Secondary request to send

20

DTR

CD

Data terminal ready

21

-

CG

Signal quality detector

22

-

CE

Ring indicator

23

-

CH / CI

Data signal rate selector

24

-

DA

Transmitted Signal element timing

25

-

-

Unassigned

In practice, the first 9-signals are sufficient for most of the serial data transmission scheme. Hence, the RS-232C bus signals are transmitted on a D-type 9-pin connector. When all the 25 signals are used, then RS-232C serial bus is terminated on a 25-pin connector.

clip_image004

Fig. 8.16 Connections used for terminating RS-232C bus

The voltage levels used for all RS-232C signals are :

Logic Low = -3V to -15V under load (-25V on no load)

Logic High = +3V to +15V under load (+25V on no load)

Commonly used voltage levels are,

+12V (Logic high) and -12V (Logic low)

• The RS-232C signal levels are not compatible with TTL logic levels.

• For interfacing TTL devices, level converters or RS-232C line drivers are employed.

• The popularly used level converters are :

1. MC 1488 - TTL to RS-232C level converter.

2. MC 1489 – RS-232C to TTL level converter.

image

MAX 232 is a bidirectional level converter. It is equivalent to a combination of MC 1488 and MC 1489 in single IC

Comments

Post a Comment

Popular posts from this blog

80386 pins and signals , 80386 modes , 80386 system design and 80386 i/o

By -
Image
11.3.5 80386 Pins and Signals The 80386 contains 132 pins in Pin Grid Array (PGA) or other packages. Figure 11.2 shows functional grouping of the 80386 pins. A brief description of the 80386 pins and signals is provided in the following. The # symbol at the end of the signal name or the- symbol above a signal name indicates the active or asserted state when it is low. When the symbol # is absent after the signal name or the symbol- is absent above a signal name, the signal is asserted when high. The 80386 has 20 Vcc and 21 GND pins for power distribution. These multiple power and ground pins reduce noise. Preferably, the circuit board should contain VCC and GND planes. CLK2 pin provides the basic timing for the 80386. This clock is then divided by 2 by the 80386 internally to provide the clock used for instruction execution. The 80386 is reset by activating the RESET pin for at least 15 CLK2 periods. The RESET signal is level­ sensitive. When the RESET pin is asserted, the 8038...
Read more

Multi-Tasking and Real-Time Operating Systems:Random Number Generator

By -
Image
PROJECT 10.2—Random Number Generator In this slightly more complex RTOS project, a random number between 0 and 255 is generated. Eight LEDs are connected to PORTB of a PIC18F452 microcontroller. In addition, a push-button switch is connected to bit 0 of PORTD (RD0), and an LED is connected to bit 7 of PORTD (RD7). Three tasks are used in this project: Live, Generator, and Display. • Task Live runs every 200ms and flashes the LED on port pin RD7 to indicate that the system is working. • Task Generator increments a variable from 0 to 255 continuously and checks the status of the push-button switch. When the push-button switch is pressed, the value of the current count is sent to task Display using a messaging queue. • Task Display reads the number from the message queue and sends the received byte to the LEDs connected to PORTB. Thus, the LEDs display a random pattern every time the push button is pressed. Figure 10.9 shows the project’s block diagram. The circuit diagram is ...
Read more

Advanced PIC18 Projects—SD Card Projects:Using the Card Filing System

By -
Image
PROJECT 7.3—Using the Card Filing System The hardware of this project is the same as for Project 7.1 (i.e., as shown in Figure 7.8). In this project, a file called MYFILE55.TXT is created on the SD card. String “This is MYFILE.TXT” is written to the file initially. Then the string “This is the added data.. .” is appended to the file. The program then reads the contents of the file and sends the string “This is MYFILE.TXT. This is the added data.. .” to the UART, enabling the data to be displayed on the PC screen when HyperTerminal is run. The program listing of the project is given in Figure 7.12 (program SD3.C). At the beginning of the program the UART is initialized to 2400 baud. Then the SPI bus and the FAT file system are initialized as required by the library. The program then creates file MYFILE55.TXT by calling library function Mmc_Fat_Assign with the arguments as the filename and the creation flag 0x80, which tells the function to create a new file if the file doe...
Read more