appendixg (cabling diagram serial video keyboard)

8/18/2019 Appendixg (Cabling Diagram Serial Video Keyboard)

1/14

CablingDiagrams: Serial,Video, Keyboard,Parallel, Network

and More

This appendix is probably the most technical offering inthis book. It contains diagrams for five common datacables and three common connectors used to interconnectPCs, modems, printers, and other peripherals through serialand parallel ports. A sixth cable, a parallel null modem, is use-ful as an extra cable between two systems using LapLink orsimilar direct-connection PC file transfer programs, which cantransfer data between PCs through parallel printer ports attwo to five times the rate of serial ports.

Connections are also listed for the four common video stan-dards used on PCs—Monochrome, Color Graphics Adapter(CGA), Enhanced Graphics Adapter (EGA), and Video GraphicsArray (VGA)—and for PC keyboard cables. We’ve also includeda special circuit that can save your modem and possibly yourPC system from excessive voltage that may appear on yourtelephone line during storms or other electrical disturbances.

GGA P P E N D I✦ ✦ ✦


2/14

768 Appendixes

Special Serial ConnectionsMany of the cables shown in the figures can be bought off the shelf at computer

or electronics stores. All too often, we have found that there are three or four varia-tions of null modems that are not correct. The null modem shown here is correct. If you have to build a cable, many snap-in wires and connectors are available that takeonly a few minutes to assemble with simple tools and no soldering. Refer to Chapter20 for the specific details of each signal pin.

Our first diagram, Figure G-1, is for a proper 25-pin-to-25 pin serial null modem cable. Anull modem cable is used to interconnect two PC systems for the purpose of transfer-ring files or for remote operation of another PC. With some printers or other devices, anull modem is required to swap signals to their proper pins to enable devices to workproperly with your PC.

Figure G-1: A 25-pin-to-25-pin null modem

This is a full-function null modem, providing all the proper hardware handshakingand device status signals. Many null modems offered for sale or built by hand incor-rectly connect the carrier detect signal to the standard hardware-handshake signallines, or they loop the handshaking signals back to the originating device. These mis-wirings can cause loss of data or failure of information transfer. Properly built, onedevice should provide active signals to the other, whether the signal is a “ready” lineor a “send” line. Looping signals from a device back to itself provides no informationto another device—both will try to operate independently, and data loss can result.

1

2

3

4

5

6

7

8

20

1

2

3

4

5

6

7

8

20

22

Request to send

Data terminal ready

Signal common

Frame /ground

Transmit data send

Receiving data

Clear to send

Data set ready

Carrier detect

Ring indicator


3/14

Appendix G ✦ Cabling Diagrams

The rules of proper interconnection are applied to the 25-pin-to-9-pin and the 9-pin-to-9-pin null modem cabling diagrams (Figures G-2, G-3, and G-4).

The numbered pin connections shown are valid whether the connectors are maleplugs or female sockets. The pin orientations for each type of connector are shownat the end of this appendix.



1

2

4

5

6

7

8

9

3

2

3

5

6

7

8

9

4

Transmit data

Clear to send

Data set ready

Carrier detect

Receive data

Data terminal ready

Signal common

Request to send

Ring detect

1

Request to send

Data terminalready

Signal common

Frame /ground

Transmit data

Receive data

Clear to send

Data set ready

Carrier detect

Ring detect

N/C1

2

4

5

6

7

8

20

3

2

3

5

6

7

8

9

4

22

Transmit data

Clear to send

Data set ready

Carrier detect

Receive data

Data terminalready

Signal common

Request to send

Ring detect

N/C

N/C

1


4/14

770 Appendixes

Figure G-4: A 25-pin-to-9-pin adapter

Video Adapter to Monitor Cabling Tables G-1 through G-4 show the pin connections for monochrome, Color GraphicsAdapter (CGA), Enhanced Graphics Adapter (EGA), and Video Graphics Array(VGA) display adapter to monitor cabling. Notice that the monochrome, CGA, andEGA cables use the same type and polarity of connector to attach to the displayadapter. Because these cables use the same connections and there is no way to

tell the difference between monochrome, CGA, or EGA display adapters from theconnections, the connections on a PC can be confusing. Do not guess at the typeof display adapter inside a PC. You will have to inspect the display-adapter cardfor markings or part numbers and seek technical support if it is not obviouswhich display adapter a system has.

Table G-1Monochrome Display Monitor and Adapter Connections

Pin Number Signal

1 Ground

2 Ground

3 n/ c

Request to send

Data terminal ready

Signal common

Frame /ground

Transmit data

Receive data

Clear to send

Data set ready

Carrier detect

Ring detect

N/C1

2

4

5

6

7

8

20

3

3

2

8

6

5

1

4

9

7

22


5/14


Pin Number Signal

4 n/ c

5 n/ c

6 Intensity bit

7 Video bit

8 Horizontal sync +

9 Vertical sync +

Table G-2Color Graphics Display Moni tor and Adapter Connections

Pin Number Signal

1 Ground

2 Ground

3 Red signal

4 Green signal

5 Blue signal

6 Intensity signal

7 n/ c

8 Horizontal sync

9 Vertical sync

Table G-3Enhanced Graphics Adapter and Monitor Connections

Pin Number Signal

1 Ground

2 Secondary red

3 Red signal

4 Primary green

5 Primary blue

Continued


6/14

772 Appendixes

Table G-3 (continued)

Pin Number Signa l

6 Secondary green

7 Secondary blue

8 Horizontal sync

9 Vertical sync

Table G-4Video Graphics Array Moni tor and Adapter Connections

Pin Number Signa l

1 Red video

2 Green video

3 Blue video

4 Monitor ID bit 2

5 Ground

6 Red return

7 Green return

8 Blue return9 Key—no pin

10 Sync return

11 Monitor ID bit 0

12 Monitor ID bit 1

13 Horizontal sync

14 Vertical sync

15 Not used


7/14


Keyboard ConnectionsMost PCs use a standard 5-pin circular DIN connector for the keyboard-to-mother-

board connections. Many newer systems, as well as the IBM PS/2 and later series,use a mini-DIN plug. The PS/2-style pointing devices use the same connections asthe PS/2-style keyboard connectors (as shown in Table G-5).

Table G-5Standard and PS/ 2 Keyboard Connectors

Signa l Standard PC Pin Num ber PS/ 2-Style Signal Pin Number

Clock 1 5

Data 2 1Ground 4 3

+5 VDC 5 4

Not used 3 2 and 6

Parallel Port Cable Diagrams The IBM PC parallel port has seen many uses from driving signals into a basic dot-matrix printer to being used as an interface for external disk drives, tape drives,

and scanners. The basic cabling diagram connecting a DB-25 male plug to aCentronics 36-pin male plug is shown in Table G-6.

Table G-6Standard PC Printer Cable Connections

DB25 out connector p ins Name

1 => 1 -Strobe

2 => 2 Data 03 => 3 Data 1

4 => 4 Data 2

5 => 5 Data 3

Continued


8/14

774 Appendixes

Table G-6 (continued)

DB25 out connector p ins Name

6 => 6 Data 4

7 => 7 Data 5

8 => 8 Data 6

9 => 9 Data 7

10


9/14


DB25 Male Pin # Connect ion DB25 Male Pin #

4 1000 ohm resistor 4






10 wire 1

11 wire 14

12 wire 16

13 wire 1714 wire 11

16 wire 12

17 wire 13

18–25 wire 18–25

The 1000 ohm resistors in series with each of the data lines on pins 2–9 are optionalin some configurations. They condition and protect signal lines on the driver chipson each end of the connection inside the PC. All other connections are a straight-

through wire. Each signal line should be a twisted pair with the ground lines on pins18–25, doubling up with the grounds from the nondata lines on pins 10–17.

Common PC Connector DiagramsFigure G-5 shows the orientation and pin numbering of both the male plug andfemale/socket of bare connectors. Because most of the wiring you might do withthese connectors is done from the wire or backside of the connectors, we empha-size that side here.

PC systems usually have female/socket connectors for the video and parallel printercables andmale/plug connectors for the serial ports. Only a few odd systems makeany change to this convention, and the change is typically the use of a female con-nector for the serial port. You may also find that the wiring is completely reversedfor these serial ports, requiring a null modem cable or signal swap to enable inter-connected devices to work properly.

Figure G-6 contains diagrams of the 9- and 25-pin serial loopback connectors thatmay be used for most diagnostic programs and the 25-pin parallel port loopbackplug for DiagSoft’s QAPlus diagnostic products.

Note


10/14

776 Appendixes

Figure G-5: 9-, 25-, and 36-pin connector layouts

Figure G-6: Typical diagnostic loopback plugs

14

15

17

1

2

3

4

5

6

7

8

9

10

11

12

13

Parallel Port Test Plug

1

2

3

4

5

6

7

8

14

15

16

17

18

19

20

21

22

25-Pin Serial Test Socket

1

2

3

4

5

6

7

8

9

9-Pin Serial Test Socket

25 24 23 22 21 20 19 18

14 15 16 17 18 19 20 21

17 16 15 14

22 23 24 25

7

male

female

pin 1 pin 1on maleconnector

on femaleconnector

9 8 7 6

6 7 8 9

3

Connector

face

Wiring

side

RS-232 Serial Port Connectors


11/14


Save Your ModemFigure G-7 shows a simple but effective protection circuit you can use with your

modem, fax, or answering machine. This circuit is not FCC- or AT&T/Bell Systems-approved. Many modems, answering, and fax machines, as well as electronic andstandard telephones, provide some form of internal protection against excessivevoltage appearing across the phone lines. Unfortunately, the ratings for these protec-tion devices are not always adequate for the line conditions you might encounter.

The standard protection is for short-duration voltages in excess of 400 volts.Sustained voltages greater than 150 to 200 volts may damage many circuits.

Figure G-7: Modem protector diagram

Theoretically, the voltage on your phone lines should never exceed 130 volts AC. This is the potential of the voltage that activates a ringer, a beeper, or a modem’sring detect circuit. The normal idle line voltage (phone on hook, no ringing) for atelephone line is 48 volts DC. This drops to between 6 and 24 volts when the line isin use. The devices you plug into a phone line should be able to operate at theselevels. Lightning can impress well over 1,000 volts on the phone line, which can eas-ily destroy delicate electronic equipment or your PC if this high voltage gets inside.

47 ohm 47 ohm

47 ohm 47 ohm

130 voltMOV

(metal-oxide-varistor)

0.01 ufd1,000 volts To modem To line

MOV .01 Capacitorred red

green greenRJ -11 plug RJ -11 plug

Resistors

Copyright 1989-91 J im Aspinwall


12/14

778 Appendixes

Some phone systems, connected between outside lines and a telephone set, can pre-sent different voltages at different times and may not be suitable for your modem. If you can prevent high voltages from reaching your equipment, it will suffer little or nodamage. We recommend you use this circuit or a similar one if you anticipate connect-ing your modem to unfamiliar phone systems. If the phone system is not designed formodems, the circuit won’t make your modem work with the line, but it can prevent itfrom being damaged.

The circuit shown in Figure G-7 was designed for a private, in-house phone systemnot directly attached to phone company circuits. It is an alternative to the expen-sive and less functional off-the-shelf units that costs ten times as much. It can alsodramatically reduce line noise that can cause data errors. If your system or add-onsare susceptible to high voltage damage, and most are, you may want to try this cir-cuit. This device is easy to build inside a common modular phone jack unit usingparts available at most neighborhood electronics stores.

This device is not certified by the FCC or by telephone companies for use on stan-dard direct lines. Its use on direct lines may violate your local telephone companyor state tariffs. It does not damage lines or equipment, nor does it degrade the per-formance of your lines or equipment. In most cases, it improves the clarity and itcertainly adds to the protection of equipment.

The four resistors help to slightly reduce the normal line current and absorb most of the excess energy of voltages over 130 volts. The metal-oxide-varistor (MOV) is theprimary protection device. It sets the limit for the voltages that can pass betweenthe line and the equipment. The 0.01 microfarad capacitor works with the resistorsto reduce signals above the voice audio range (3 kHz). This has the effect of reduc-ing clicks, pops, and static on the line.

If the resistors are replaced with 10 microhenry, 100 milliampere inductors, this cir-cuit will provide much the same voltage protection and severely reduce any radiointerference. Further reduction of radio interference may require the addition of a0.001 microfarad capacitor from each end of the MOV to a solid nearby groundpoint. Using the capacitors and inductors is a long-standing method of removingradio interference (which is allowed and common in severe cases) as a repair orcorrection to phone lines. In effect, either circuit method should be allowed to beused as a repair if line noise is in excess of any standard limits.

Reducing the capacitor value from 0.01 microfarad to 0.0001 microfarad (100 pico-farad) and changing the connectors to RJ -45 (6-pin) or RJ-48 (8-pin) will enable you

to use this device on Integrated Services Digital Network (ISDN) interface units oneither ISDN connection type S (requires separate NT-1 device) or U (NT-1 deviceincluded in unit).

10BaseT Network ConnectionsMost network connections today make use of economical twisted-pair cablingand connectors similar to those used for phone lines. However, the placement or


13/14


attachment of the wires into the connectors is different to accommodate Ethernetuse. You cannot reliably use a straight-through 8-pin or RJ-45 telephone cable forhigh-speed network cabling. The following diagrams, Figures G-8 and G-9, illustratethe pins and wire colors used for network cabling.

Figure G-8: Standard 10BaseT interconnections for connecting systems and devicesto a hub

Figure G-9: Crossover 10BaseT interconnections for connecting two systemswithout a hub

✦ ✦ ✦

876543

21

876543

21

BrownBrown/White

GreenBlue/White

BlueGreen/White

OrangeOrange/White

BrownBrown/WhiteGreen/WhiteBlue/WhiteBlueGreen

Orange/WhiteOrange

Green & Orange pairs crossover each otherEnd End view

Clip

Signal Reference Normal Crossover

n/a 8 8 8

n/a 7 7 7

Transmit- 6 6 2

n/a 5 5 5

n/a 4 4 4

Transmit+ 3 3 1

Recieve- 2 2 6Recieve+ 1 1 3

87654321

87654321

BrownBrown/White

GreenBlue/White

BlueGreen/White

OrangeOrange/White

BrownBrown/WhiteGreenBlue/WhiteBlueGreenOrangeOrange/White

Each pair is wired PIN-PINEnd End view

Clip


14/14

appendixg (cabling diagram serial video keyboard)

Documents