CPU/NIBP Module Assembly with LCD Display Theory of Operation
1 - 8 0070-10-0691 Accutorr Plus Service Manual
1.2.4.9 Communication Block
The module provides the following interfaces and functions:
• RS-232E drive from TTL levels. RS-232E driver for CIS/HIS that will provide
minimum of 9V signal level.
• IC based DC/DC converter capable of converting VCC to 12VDC, with leakage
current when off < 100uA. High frequency operation to limit emitted fields. Capable of
providing an output current of 125 mA @ 12Vdc, with an efficiency of 80% or higher.
• Signal driver for an external isolated relay that will be used for Nurse Call, provided on
pins of the 9-pin RS-232 connector.
The RS-232E interface required is implemented using a Maxim, MAX236 Multi-Channel
Transceiver (U602). This chip was chosen because it has a minimum ±9 volt output signal
level. Communication is to support a 5 wire interface, 4 signals and a ground. The signals
are described below:
All RS-232 signals are ESD protected by a U603, an SM14M24C Transient Voltage
Suppressor array. The +12 VT dc power required by the Nurse Call cable is supplied from
the onboard DC/DC converter. The MAX236 receivers are controlled by logic signal
CSTAT*. Logic 0 enables the receivers; otherwise, they are tri-stated.
The RS-232 signals appear on connector J603, a dual row 14 pin header which will have a
mating 14 pin pendant ribbon cable attached. The other end of the ribbon cable assembly
is a 9 pin panel mount ‘D’ connector.
1.2.4.10 Backlight LED Driver
The LED driver module is implemented with Linear LT3474, step-down 1A LED driver. It
can source constant current maximum up to 1A. The current can be programmed by
setting the voltage at Vadj pin (pin 13) through resistors R42 and R14. The switching
frequency is programmed to 300KHz for best duty cycle (i.e, 96%) for higher efficiency.
The typical LED drop voltage of 3.5V is achieved by programming the constant output
LED current of 71mA. The Vadj is sourced from external voltage source (i.e., +5V VCC)
by external resistor divider.
1.2.4.11 LCD Trend Display
DAC control provided from the LED/Tone Board controls the LCD View Angle.
SIGNAL DESCRIPTION INPUT/OUTPUT
RXD Received Data from DCE to
DTE device
Input
TXD Transmitted Data from DTE
to DCE device
Output
RTS Request to send from DTE
to DCE device
Output
CTS Clear to Send from DCE
device
Input
GND Signal Ground Input
To Next Page
Loading...