NAL A3LA-R, Руководство пользователя

Страница: 21 / 158

A3LA-R User Guide Version A
Document Number: 451-93156-001A 21 of 158
may not operate and the A3LA-R could be placed in a non-operational state. The state is not
permanent and can be rectified by the above procedure.
The EXT_ON_OFF pin can be connected to an external I/O control line to turn a powered
A3LA-R on and off in a toggle fashion. With this setup, the EXT_ON_OFF line MUST first be held
to GND level (i.e., logic low) before applying power to the A3LA-R. As long as DC power input is
applied, logic high on the EXT_ON_OFF line turns the A3LA-R on, and a logic low turns it off.
Logic high is defined as having a voltage ranging from 2.0 V to 5.0 V—DO NOT allow logic high
to exceed 6 V. Logic low can range from –0.3 V to 0.8 V. The current drawn on the external load
used to pull the A3LA-R to GND is no more than 20 μA. The A3LA-R draws approximately 20 mA,
even when turned off. Thus, DC power must be removed to eliminate any parasitic current
drawn. Damage may be caused to the A3LA-R if EXT_ON_OFF is high and DC power is not
present. Ensure that this condition does not occur.
2.5 A
UDIO
I
NTERFACE
The A3LA-R supports both digital and analog audio I/O. The digital audio is in PCM format. In
such format, digital audio cannot travel far (less than one foot); this is why the analog is chosen
for the A3LA-R audio handset. The analog audio input is a single-ended, unbalanced input with
a minimum impedance of 10 kΩ to ground. The A3LA-R accepts a maximum input level of 2.0 V
peak-to-peak without signal distortion. The analog audio output is also a single-ended,
unbalanced output capable of driving an impedance of 600 Ω or more to ground. The A3LA-R
delivers undistorted audio up to 2.0 V peak-to-peak at this port.
The combined analog I/O audio interface (pins 5 and 15) and the DPL UART I/O interface (pins
18 and 20) enable an analog audio handset to be connected to the A3LA-R. With the DPL audio
handset model DPLS0401-X and DB25 data kit model HRC-24-8R, the A3LA-R can be used both
as a data modem and a satellite phone. This setup, as shown in Figure 3 , can be an extremely
useful developmental tool because the modem status can be seen on the handset LCD, similarly
to a 9555 Iridium phone.