Datex-Ohmeda Aestiva 7900 SmartVent, Technical Reference Manual

Page: 35 / 204

2 Theory of Operation
1006-0453-000 05/04 2-19
Front panel display interface
All signals to and from the Front Panel are protected from ESD through the use
of transient suppression devices and appropriate filtering. All of these signals
are routed through a single connector from the microcontroller board to the
front panel assembly.
EL display controller
The S-MOS SED1351F flat panel display controller drives 480 horizontal
pixels by 240 vertical pixels of the EL display. Ferrite beads filter the signals
from the display controller to the display.
Video display memory
This memory consists of one high speed 32K x 8 CMOS static RAM directly
connected to the display controller. The video memory is mapped into
memory space, but access is controlled by the display controller to ensure
that the EL display is not disturbed during an access by the processor.
Membrane switch inputs
These signals are electronically debounced by an RC filter and sampled by the
68340 processor.
LED driver outputs
The AC ON LED is turned on directly from the AC power applied.
Rotary encoder input
This quadrature signal is debounced and routed to a quadrature clock
converter which interrupts the 68340 processor at each detent position.
Audio alarm
The circuit consists of a programmable sound generator and a LM4860M
audio amplifier. The sound generator interfaces directly to the CPU and the
audio amplifier drives an 8 ohm speaker. It is normally powered from the low
dropout regulator using the 5.8 V supply. In the event of a loss of the 5.8 V
supply, the sound generator will be powered by the VDD supply to prevent
loading of the processor data bus.
External interface
The external interface of the ventilator is an important design task from the
standpoint of Electromagnetic compatibility (EMC). It is important to protect
the ventilator from conducted and radiated Electromagnetic Interference
(EMI) and from Electrostatic Discharge (ESD). In addition, EMI design
precautions are taken to control the emission of EMI via cabling and access
ports.
Communication interface
(RS232C)
There are two RS232C interfaces. Each channel is configured for full-duplex
asynchronous operation at communication rates up to 19.2k baud. The
isolated interfaces help eliminate the possibility of ground loops. The RS-232
inputs and outputs completely conform to all EIA RS-232C and CCITT V28
specifications.