Datascope Accutorr Plus Service Manual page 78

Keypad interface
The keypad is made up of a 3 x 8 matrix of keys. U6 will monitor the array of 8 keys. It
is pulled up and when a key is pressed, one of those lines will go low. An interrogation
will commence from the MC68302 to find which key was pressed.
Communication Interface
The Accutorr Plus Communication module provides the communication signal interface
between the LED/CPU board and the external communication interface connector. The
board supports the CIS/HIS/DIAP interface via RS-232E or RS-485, providing a feed
through path for the Datascope proprietary download connector (J1), the DC/DC converter
(for the =12Vdc @ 100mA required for wireless telemetry), and the RS-232 driver.
SpO
2
The SpO
and +5V, and ground are provided by the LED/CPU module. The MC68302, interfaces
with the SCC2692 of the SpO
sends serial information via signal, SpO
SpO _RXD. The LED/CPU module can reset the SpO
2
SpO RST*. The signal SpO
2
used to create the heart beat.
DAC functions
U22 is a dual 8 bit DAC, that interfaces to U1, MC68302. It controls the attenuation
needed for the speaker driver circuitry and the amplitude of LCD drive signal, VEE, ie.,
steps of 255 from 0 to -10.4 V minimum. The device is selected via the CS_IO* signal.
Power to the DAC is provided by an unboard DC-DC convertor. The DAC is written to
when WR_DDAC* pulses hi when CS_IO* is active low. Timing is equivalent to that
discussed in section 2.3.10.
Speaker Driver
This function is driven by the MC68302 in two manners. One is the enable signal,
TONE, and the other will attenuate the output signal in steps of 255 via the data bus,
D(0..7). TONE is a 5V signal which is divided down by 26 to 200mV and buffered by
U24, LM358. This signal is then attenuated by U22, AD7528, and buffered by the other
half of U24. U25 is the speaker driver section and this amplifier is set for a gain of 20.
LCD
The LCD drive supply voltage is specified for -10.4V minimum. It can go to a maximum
of 17V with respect to VDD logic supply voltage. The DAC, U22 will take +15VF as
reference voltage and feed that to TL032, U23, to invert to -15V output. That is then
buffered by another section of U23 and drive base of Q9. Transistor Q8 is set up as a
current limiter for Q9. It monitors the current across R32. If the voltage across R32 is
greater than 0.7V, ie., 21mA, then shunt drive voltage to the base of Q9 to limit the current.
2-16
Revised 12/20/00
Interface
module connects to the LED/CPU module via connector J7. Power, ie., æ15V
2
module through a TTL serial interface. The SpO
2
* is used to provide the LED/CPU with the systolic signal
2
_TXD, and receives information via signal,
2
module by asserting
2
Accutorr Plus Service Manual
Chapter 2 - Theory of Operation
module
2