Das Analog-To-Digital Converter Circuitry; Das Fluid Detector Circuitry; Rtp/Uip First In First Out (Fifo) Memory Communications Circuitry - Bayer HealthCare RapidPoint 400 Series Service Manual

DAS Analog-to-Digital Converter Circuitry

This section of the Main board contains the balanced low-pass filter that
eliminates and averages noise received from the multiplexers, U8 and U9.
The filter output is sent to IC U14. U14 is an instrumentation amplifier that
converts differential signals to a single-ended signal.
The ADC IC U23 is a 16-bit converter. From the converter, the output is sent
to U38 in a serial digital form. U38 converts the data from serial to parallel
and sends it to the 68332 microprocessor.
The ADC IC U23 also needs a stable reference voltage to compare the
unknown input voltage. Reference source U15 and buffer amplifier U16,
along with significant filter capacitors, create an extremely stable 5 V
source for the ADC.

DAS Fluid Detector Circuitry

This section of the Main board contains the circuitry from which the two
analog fluid detector signals are monitored. The fluid detector signals are
sent to a pair of comparators located in U17.
The non-inverting input pins of these comparators connect to a dual, 12-bit
DAC, U24. The DAC allows the comparators to have programmable trip
points, so each fluid detector has its own voltage level for comparison. The
output of each comparator is sent to U12 as digital zero- or one-bit.
This section of the Main board also contains an eight-channel, single-
ended multiplexer, U13, that monitors various system voltages, such as
DAC heater temperatures and motor reference voltages.

RTP/UIP First In First Out (FIFO) Memory Communications Circuitry

This section of the Main board contains the circuitry that allows the user
interface processor (UIP) and the RTP 68332 processor to communicate
with each other. Communication occurs using two FIFO memories, U21
and U29. U21 and U29 are cross-coupled to each data path, which allows
full communication in both directions. Status flags on both memories
indicate to the microprocessors when the FIFOs are full or empty.
86 Rev. C