Ampro Corporation 486E - Manual (Page 73)

Product Reference
2–57
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.