VT100.net VT100 Technical Manual

Chapter 3 Installation and Interface Information

Site Considerations

The design of the VT100 (Figure 3-1) normally poses few constraints on selecting a place in which to install the terminal. In most cases, any environment suitable to the operator is a satisfactory environment in which to operate the terminal. Extremes of temperature and humidity should be avoided. A summary of VT100 guaranteed operating conditions may be found in Chapter 1.

Unpacking and Installation

The VT100 shipping carton contains the following items:

To install the VT100 perform the following steps:

  1. Remove the VT100 from the shipping carton and place it in the desired work area.
  2. Place the keyboard in front of the terminal and plug the keyboard coiled cord into the keyboard receptacle at the rear of the terminal (Figure 3-2).
  3. Verify that the power selector switch shows the correct wall outlet voltage (115 V is standard in the U.S.) and the power switch is off.
  4. Connect the power cord to the power cord receptacle at the rear of the terminal and plug the other end of the power cord into a nearby wall outlet.
  5. Connect the communications cable to the appropriate communications receptacle.
  6. Turn the power switch on. The terminal automatically performs the power-up self test and either the ON LINE or LOCAL indicator on the keyboard will light. After approximately one minute the cursor will be visible in the upper-left corner of the screen.
  7. Set the desired SET-UP features outlined in the operator section of this manual.
  8. Once the installation procedure is complete, record the SET-UP features selected on the VT100 SET-UP label and attach the label to the underside of the keyboard.
Figure 3-1 VT100 Terminal Dimensions
Figure 3-2 VT100 Rear View

User Maintenance

The keyboard keys are the only moving parts of the terminal and require no preventive maintenance by the owner. The VT100 surfaces may be cleaned with soap and water or any mild detergent. Cleaners with solvents should not be used.

The VT100 packaging is not meant to be weatherproof; there are several openings in the case through which liquids, coins, paper clips, and other objects can fall. Such objects would disturb the electronic operation of the terminal if they came into contact with the circuitry. For this reason, avoid putting drinks and metal objects on the top of the terminal, or using excessive water to clean the terminal. Rubbing the keys with a dry or barely moist cloth should clean them. Do not remove the keycaps to clean them more thoroughly; damage may result to the switch contacts if they are replaced incorrectly.

Keep the ventilation slots clear. Blocking these slots by placing objects on top of or under the VT100 may cause the terminal to overheat.

Interface Information

EIA Interface

The basic VT100 operates on full duplex, asynchronous communication lines. The terminal interfaces to the line with a 25-pin connector mounted on the back of the terminal which meets the requirements of EIA specification RS-232-C. Table 3-1 summarizes the EIA connector signals. The following paragraphs explain each signal as used in the basic VT100.

Protective Ground - Pin 1

This conductor is electrically bonded to the VT100 chassis. Use of this conductor for reference potential purposes is not allowed.

Transmitted Data (from VT100) - Pin 2

The VT 100 transmits serially encoded characters and break signals on this circuit, which is held in the mark state when neither characters nor break signals are being transmitted.

Received Data (to VT100) - Pin 3

The VT100 receives serially encoded characters generated by the user’s equipment on this circuit.

Request to Send (from VT100) - Pin 4

Asserted at all times when terminal is powered up.

Carrier Detect (to VT100) - Pin 8

Ignored at all times.

Speed Select (from VT100) - Pins 11, 19, and 23

This signal is alternately called secondary request to send. The basic VT100 maintains this line in the asserted state at all times.

Speed Indicator (to VT100) - Pin 12

This signal is alternately called secondary carrier detect and is ignored at all times.

Transmission Clock (to VT100) - Pin 15

Ignored at all times.

Clear to Send (to VT100) - Pin 5

Ignored at all times.

Data Set Ready (to VT100) - Pin 6

Ignored at all times.

Signal Ground - Pin 7

This conductor establishes the common ground reference potential for all voltages on the interface. It is permanently connected to the VT100 chassis.

Receive Clock (to VT100) - Pin 17

Ignored at all times.

Data Terminal Ready (From VT100) - Pin 20

Data terminal ready is asserted at all times.

Ring Indicator (to VT100) - Pin 22

Ignored at all times.

Table 3-1 EIA Connector Signals
Pin No. Description
1 Protective ground
1 Transmitted data
3 Received data
4 Request to send
5 Clear to send
6 Data set ready
7 Signal ground (common return)
8 Carrier detect
9 (Not used)
10 (Not used)
11 Same as pin 19
12 (Secondary carrier detect) speed indicator
13 (Not used)
14 (Not used)
15 Transmit clock
16 (Not used)
17 Receive clock
18 (Not used)
19 (Secondary request to send) speed select
20 Data terminal ready
21 (Not used)
22 Ring indicator
23 Same as pin 19
24 (Not used)
25 (Not used)

Electrical Characteristics

VT100 Output Voltages

On all signals designated “from VT100,” the mark or unasserted state is -6.0 V to -12.0 V; the space or asserted state is +6.0 V to + 12.0 V.

VT100 Input Voltages

On signals designated “to VT100,” -25.0 V to +0.75 V or an open circuit is interpreted as a mark or unasserted state, and +25.0 V to +2.25 V is interpreted as a space or asserted state. Voltages greater in magnitude than 25 V are not allowed. These levels are compatible with EIA STD RS-232-C and CCITT Recommendation V.28.

Optional 20 mA Current Loop Interface

In most current loop applications, the VT100 is connected in a passive configuration - that is, current is supplied to the VT100. In this mode, the transmitter and receiver are both passive, both optically isolated, and the transmitter goes to the mark state when power is turned off.

Conversion from active to passive (or vice versa) requires moving a slide switch.

In active mode either the transmitter or the receiver or both may be connected so that the VT100 sources the 20 mA of current. In active mode isolation is not present and the transmitter goes to the space state when power to the VT100 is turned off.

Figure 3-3 shows the 20 mA current loop interface connector mounted to the access cover and lists the individual pin assignments.

The electrical characteristics of the 20 mA current loop interface are shown below.

Min Max
Open circuit voltage 5.0 V 50 V
Voltage drop marking - 2.0 V
Spacing current - 2.0 mA
Marking current 20 mA 50 mA
Min Max
Voltage drop marking - 2.5 V
Spacing current - 3.0 mA
Marking current 15 mA 50 mA

In addition to the above specifications for passive operation, active mode places the transmitter or receiver in series with a source of 17 V ± 5 percent and 660 ohms.

Figure 3-3 20 mA Current Loop Interface

External Video Connections

In addition to the EIA interface, the VT100 can easily interface to external video devices. The video devices may act either as a slave to the VT100 when connected to the composite video output or provide synchronized video to the VT100 video section when connected to the video input. The external video connectors are the two female BNC connectors located on the back of the terminal just below the EIA connector. The upper connector, J8, is the video input while the lower connector, J9, is the video output.

Composite Video Output (J9)

The composite video output provides RS170 output generated by combining the video signal with a composite sync signal. The output contains all video data appearing on the VT100 screen except that video which comes from J8. The output has the following nominal characteristics (Figure 3-4):

  1. Output impedance = 75 ohms, dc-coupled
  2. Sync level = 0 V
  3. Black level = approximately 0.3 V when loaded with 75 ohms
  4. White level = approximately 1.0 V with a 75 ohm load

The composite sync waveform conforms to EIA RS 170 standards. The vertical interval is composed of six equalizing pulses, six vertical sync pulses, and six more equalizing pulses. The timing is as follows:

Equalizing pulse width = 2.33 µs ± 50 ns
Vertical pulse width = 27.28 µs ± 200 ns
Horizontal pulse width = 4.71 µs ± 50 ns
Horizontal blank width = 11.84 µs ± 50 ns/80 column mode
= 12.34 µs ± 50 ns/132 column mode
Front porch = 1.54 µs ± 50 ns.
Figure 3-4 Composite Video Output

Video Input (J8)

An analog signal applied to the video input is “ORed” with the internal video signal such that the beam intensity at any point on the screen corresponds to the intensity of that signal which tends to make the beam brighter at that point. A video signal on this input affects only the internal screen and does not appear on the composite video output. This input has the following nominal characteristics:

  1. Input impedance = 75 ohms, dc-coupled
  2. Black level = 0 V
  3. White level = 1.0 V
  4. Maximum continuous input = ±2.0 V.

The external video source must be synchronized to the VT100; it may do this by referencing the composite sync on the composite video output. This means that the VT100 video input will not synchronize with any composite video source including the composite video output of another VT100.