PC Hardware

Serial Port Cables

A serial port allows a computer to send data over long distances by converting parallel data to serial data. Typical computers will have one or two serial ports, usually designated as COM1 and COM2. The "standard" port is a 9-pin male connector on the computer, shown in Figure 12.9. (There are also 25-pin cables available.)

Figure 12.9 Standard 9-pin D connector

The following table describes the pin connection for the 9-pin and 25-pin serial cable connectors.

9-pin 25-pin Name ID Function
1 Shield
3 2 Transmitted Data TX Data sent from computer.
2 3 Receive Data RX Data sent to computer.
7 4 Request to Send RTS Computer is ready to send.
8 5 Clear to Send CTS "Other end" is ready to receive
6 6 Data Set Ready DSR "Other end" is ready to receive.
5 7 Signal Ground SG GND.
1 8 Data Carrier Detected DCD The modem has detected a signal from another modem.
4 20 Data Terminal Ready DTR Computer is ready to send.
9 22 Ring Indicator RI Modem detects line ringing.

Null-Modem Cables

Null-modem cables are used to directly connect two computers together without the need for a modem. The transmit and receive wires in the cable (wires 2 and 3) are switched to make the computers "think" they are using modems.

SCSI Cables

SCSI cables come in a variety of sizes depending on the type of SCSI used and the manufacturer of the device. Typically, internal cables are flat ribbon types and external cables are shielded bundles.

SCSI Cables

SCSI cables come in a variety of sizes depending on the type of SCSI used and the manufacturer of the device. Typically, internal cables are flat ribbon types and external cables are shielded bundles.

Keyboard Cables

Another peripheral device with a cable that we encounter and yet never think about is the keyboard. Because there are different types of keyboard cables (and connectors) and because, on occasion, the technician might encounter a problem with a keyboard connector, they are worthy of mention.

Keyboards are manufactured in two different styles with different cables and connectors. Earlier versions used a 5-pin DIN connector (DIN stands for Deutsche Industrie Norm, the German national standards organization), and most new keyboards use a 6-pin DIN connector, the same as is used on a PS/2 mouse. Connectors are available to convert the 5-pin DIN to a 6-pin mini-DIN. Although they have a different number of pins, they use the same wires and pin outs. Data is sent serially to the keyboard using the keyboard interface. Data is written to the controller's input buffer to accomplish this. Keyboard data passes through pin 2 of the connector, while clocking signals move through pin 1. A keyboard reset, which can be connected to the system's reset line, is included at pin 3. Ground and +5-volt DC connections are applied to the keyboard through pins 4 and 5.

by BrainBellupdated
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