Ampro Corporation 486E manual PC Speaker, LED Connection, Push Button Reset Connection

Product Reference

PC Speaker

The Little Board’s motherboard logic includes a standard AT-compatible speaker port. The speaker logic signal is buffered by a transistor amplifier, and provides about 100 mW on J16-9 to an external 8-ohm speaker. Connect the other side of the speaker to ground, J16-10.

The audio output is based on two signals: the output of Timer 2; and the programming of two bits, 0 and 1, at I/O port 61h. Bit 1 of I/O port 61h is one term of a 2-input AND gate. The other term is the output from Timer 2. Thus, setting bit 1 to logic 1 enables the output of Timer 2 to the speaker, and logic 0 disables it. Disabling Timer 2 by setting bit 0 of port 61h to a 0 causes its output to go high. Then, use bit 1 of port 61h to control the speaker directly.

LED Connection

To connect an external LED power-on indication lamp, connect the LED anode (-) to J16-7 and the cathode (+) to ground. J16-7 provides +5V through a 300 ohm resistor.

Push Button Reset Connection

J16-1 provides a connection for an external normally open momentary switch to manually reset the system. Connect the other side of the switch to ground. The reset signal is “de-bounced” on the board.

Keyboard Connections

An AT (not PC) keyboard can be connected to the keyboard port. J16-13 through J16-16 provide this function. Normally, AT keyboards include a cable that terminates in a male 5-pin DIN plug for connection to an AT. Table 2–44 lists the keyboard connector pinout and signal definitions, and includes corresponding pin numbers of a normal AT DIN keyboard connector.

Table 2–44. Keyboard Connector (J16)

J16 Pin	Signal Name	DIN Pin
14	Keyboard Clock	1
13	Keyboard Data	2
N/C	No connection	3
15	Ground	4
16	Keyboard power	5

External Battery Connections

To connect an external battery, connect its positive terminal to J16-17 and its negative terminal to J16-18. Use a 3.6-volt lithium cell.

The battery is connected by a low-drop Schottky diode. Two blocking devices are in series with the battery, complying with UL recommendations for lithium batteries.

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