Fresenius Medical Care 4008 E Technical Manual page 363

Analog inputs (circuit diagram 1/6)
All of the analog inputs are designed for an operating range of 0 to 10 V. Each of these input
signals is adapted to the integrated analog-to-digital converter (AN0 to AN7) of the 80C535 via a
voltage divider with 12.1-kOhm/10-kOhm resistors and an impedance transformer (IC1 and IC2,
LM324N – quadruple OP).
The 5-V reference voltage (UREF_5V) required for the A-D converters is derived from the 12-V
voltage supply via voltage divider R1/R2 (43.2 K/30.1 K). The two following operational amplifiers
(IC 3, LM324N) are used as impedance transformers. They deliver the current required for the
integrated A-D converter of the 80C535 microcontroller and supply further A-D converters on the
input board P.C.B. LP 633 via the contact strip x632/C30.
Digital inputs (circuit diagram 2/6)
All of the digital inputs are each connected to a voltage divider. These voltage dividers are used
to adapt different signal voltages (24 V, 12 V, 5 V) to the system of P.C.B. LP 632.
Values are as follows:
– 178.0 kOhms/47.0 kOhms for the 24-V signals,
– 66.5 kOhms/47.0 kOhms for the 12-V signals.
– The values for the 5-V signals (TTL level) are directly applied to the inputs of the drivers. Here,
the resistors provided have been replaced by bridges.
Via IC 4 and IC 5 (74HC541), the input signals are directly made available to the microcontroller
at port 4 and port 1. IC 6, IC 7, IC 8, IC 9, and IC 10 (74HC541, TRI-STATE BUFFER) are used
as bus drivers in the system. The processor has access to these drivers and inputs via specific
addresses (chip-select signals).
The two DIP SWITCHES SW1 and SW2 are provided for the basic adjustment of the hemodialy-
sis machine or for the adjustment of its optional equipment.
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Fresenius Medical Care 4008 4/09.03 (TM)