Embedded Systems: An Integrated Approach by Pearson

182 EMBEDDED SYSTEMS

for normal PC communications, and indeed, most PCs are equipped with male D type

connectors having only 9 pins. Figure 5.23 shows the DB-9 connector and Table 5.2

describes the pin functions of the DB9 connector. But again, even though the standard

connectors have 9 pins, serial communication is possible with just 3 pins: T × D, R × D

and ground. See Figure 5.24 which shows two serial ports (on two devices, say a PC and

an embedded board) connected through a three wire cable.

12 3 4 5

67 89

Figure 5.23 | The DB-9 connector

Vcc

C1

+

C3

+

C4

C2

+

2

6

1mF

1mF

1mF

1mF

1

3

4

5

11

10

12

9

From CMOS or TTL

To CMOS or TTL

15

16

14

7

13

8

RS-232 Output

RS-232 Output ...