Specifications

EPC-33/34 Hardware Reference
Page 36
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Diode and/or resistor protection is employed in accordance with UL1950/EN0950
requirements to prevent damage from reverse current.
Speaker
A very small speaker (0.5" [12.7 mm] maximum) is installed on the PCB and
connected to the standard PC "beep" generation circuit. It is expected that in high-
noise situations a larger external speaker would be connected.
The external speaker is driven with a 5V P-P square-wave signal, with current
limiting resistors. The speaker may be connected directly to either a piezoelectric
speaker or an electromagnetic speaker.
Miscellaneous function connector
A 14-pin standard 0.100" [2.54 mm] center header connector is provided to allow
access to several miscellaneous functions of the CPU card. These functions include
the following:
Speaker A signal is provided to allow the user to connect an external
speaker to the circuit provided on the CPU board to
generate sound.
HDD access LED A signal is provided for the user to connect an external LED
to indicate hard disk drive access. An external current-limit
resistor is not required; current is limited by a 330 ohm
resistor to VCC.
Power on LED A signal is provided for the user to connect an external LED
to indicate that power is applied to the system. An external
current limit resistor is not required; current is limited by a
330 ohm resistor to VCC.
Reset switch An input is provided for the user to connect an external,
SPST-NO switch to provide a reset input to the system.
This signal may also be driven with an open-collector TTL
signal.
Key switch input An input is provided to port P17 of the keyboard controller.
This is normally connected to a keylock switch to disable
the keyboard in the PC/AT system. This input has an
internal pullup resistor to VCC.