Specifications

CHAPTER 1

Introduction

16 Keyboard

Microphone 1

The Macintosh LC 520 computer has a built-in microphone at the front of the case. The

microphone is connected internally to the main logic board.

The user selects the built-in microphone as the sound source by using the Sound control

panel. For more information, see the section “Sound Control Panel” beginning on

page 41.

Sound Input Jack 1

There is a sound input jack on the back of the computer for connecting an external

microphone or other sound source. The sound input jack accepts a standard

/8-inch phone plug, either monophonic or stereophonic (two signals plus ground).

The sound input jack accepts either the external microphone for the Macintosh LC 520

computer or a pair of line-level (ampliﬁed) signals. When the user selects the

corresponding input device in the Sound control panel, the computer sets the gain

appropriately. The internal circuitry mixes the pair of stereophonic signals into a

monophonic signal.

Note

The external microphone requires power from the main computer, which

it obtains by way of an extra-long, 4-conductor plug that makes contact

with a 5-volt pin inside the sound input jack. ◆

Sound Control Pushbuttons 1

The Macintosh LC 520 computer has two pairs of pushbuttons on the front panel. The

pair of buttons on the right controls the sound level: pressing the top button causes the

level to increase, and pressing the bottom button causes the level to decrease. (The left

pair of pushbuttons controls the intensity of the display.) If the computer is playing a

sound when you press one of the sound control pushbuttons, the sound level changes as

long as you continue to press the button. If no sound is playing when you press a sound

control pushbutton, the computer plays an alert sound to conﬁrm the new level setting.

Keyboard 1

The Macintosh LC 520 computer comes with a separate keyboard like the one used with

the Macintosh Color Classic. The keyboard has a power key, identified by the symbol p.

There are no programmer’s switches on the Macintosh LC 520 case, so the reset and NMI

functions are generated by pressing the power key on the keyboard while holding down

other keys, as shown in Table 1-6. The Command key is identiﬁed by the symbols 

and x.