Orban OPTIMOD-FM 8700, Operating Manual

Page: 311 / 390

OPTIMOD-FM DIGITAL TECHNICAL DATA
6-9
1. Remote Interface and RS-232 Interfaces
Located on base board
A remote interface connector and circuitry implements remote control of certain
operating modes; OPTIMOD-FM 8700i has eight remote contact closure inputs.
A valid remote signal is a momentary pulse of current flowing through remote
signal pins. Current must flow consistently for 50msec for the signal to be inter-
preted as valid. Generally, the 8700i will respond to the most recent control op-
eration, regardless of whether it came from the front panel, remote interface, or
RS-232.
Component-Level Description:
After being current limited by resistors, the GPI control signals are applied to
two quad optoisolators, U10, 12, and then to the control circuitry.
Octal driver U1 buffers the RS-232 port, which is located on a small daughter
board.
U10, 12 and U1 are socketed for easy field replacement in the event of over-
load, lightning damage, etc. All other circuitry is surface-mount and is not
field-repairable.
2. Color LCD Display
The 5.7” color LCD is an active-matrix quarter-VGA panel. The CPU addresses its con-
troller chip through the CPU’s ISA bus.
The backlight on the display has a finite lifetime (normally a few years of continuous
operation). Therefore, the 8700i always implements a screen-saver timeout. This is
not user-adjustable.
Input Circuits
This circuitry interfaces the analog and digital inputs to the DSP. The analog input
stages scale and buffer the input audio level to match it to the analog-to-digital
(A/D) converter. The A/D converts the analog input audio to digital audio. The digi-
tal input receiver accepts AES3-format digital audio signals from the digital input
connector and sample rate-converts them as necessary. The digital audio from the
A/D and SRC is transmitted to the DSP.
1. Analog Input Stages
Located on Input/output board
The RF-filtered left and right analog input signals are each applied to a floating,
balanced amplifier. The amplifier’s output feeds a circuit that scales, balances,
and DC-biases the signal. This circuit feeds an RC low-pass filter that applies the
balanced signal to the analog-to-digital (A / D) converter.