Theory of Operations
2–5
2.6 Trend Download board (RS-232)
Transformer driver
Transformer +5 V regulator
X1
Board ID
Low speed
Opto-isolation
X2
Alarm event
relay
RS-232 driver
High speed
Opto-isolation
Trend flash
Figure 2-4. Trend Download board block diagram
The Trend Download board provides an interface for connecting a personal computer
or printer to the monitor. It contains a board ID circuit, a flash memory IC for trend
storage, an isolation transformer for isolated power, a 2500 VAC isolation barrier to
SIP/SOP, an RS-232 level translator, and a Normally-Open Reed Relay contact used
for alarm event annunciation.
The Trend Download board is powered by an isolated power supply consisting of a
switching transformer that runs at 250 KHz, a 2500 VAC isolated transformer, and
circuitry that provides 6.5 VDC raw voltage output to the secondary. A regulator
provides a 5 VDC regulated supply for the secondary. The regulator delivers 1 A of
current, but the secondary typically draws 10 mA (40 mA when the alarm event relay
is energized).
The board ID circuit identifies the configuration of the Trend Download board. When
no jumpers are installed (default configuration), a 1.5 VDC output is read by the
microcontroller on the System board. On future Trend Download boards, the output
will depend on the location of jumpers.
Up to 48 hours of trend data can be stored in a 2 MB (256K X 8) flash memory IC on
the Trend Download board through an SPI bus interface on the System board. The
flash memory buffer ensures data retention without battery backup.
All RS-232 signals are translated to a ± 7 V level by a chip with a built-in power
supply that generates ± 7 V from a single 5 VDC power input. Two high-speed opto-
isolators are connected to the RS-232 RXD and TXD signals. Two low-speed opto--
isolators are connected to the RS-232 CTS and RTS signals.
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