Fresenius Medical Care 4008 E Technical Manual page 470

Digital control unit
Together with the dual operational amplifier and various passive components, the microcontroller
and the gate array constitute the digital control unit.
The gate array is provided as customer-specific integrated circuit. It comprises the following
functions:
8-byte RAM
This RAM is provided as expansion of the microcontroller RAM.
4-digit display controller
Up to four seven-segment displays can be energized by the integrated display controller.
Three displays with a joint cathode are incorporated in the heparin pump.
The cathodes of the three displays are connected to the column connectors S00 to S20 of the
gate array; the segments are connected to the respective connectors via variable multipliers. S30
is connected to the cathodes of the two control LEDs. The anodes are applied to the segment
connectors SA0 to SF0 via variable multipliers. The display controller uses the multiplex method
to operate the displays.
8-bit port A and 4-bit port B
Port A and port B are bidirectional ports with integrated data directional registers.
The hexagonal coding switch (selection of syringe type) is connected to ports PA.0 to PA.3; the
Hall sensor provided for end position recognition is connected to port PA.5.
Port PA.7 emits the signal for reversal from full-step to eighth-step operation and vice versa to the
stepper motor controller.
Port B is not utilized.
Key encoder for 16 keys
By means of the key encoder, 16 keys can be operated in a 4x4 matrix in multiplex operation.
In addition to a 64-mS debouncing unit, an N-key-rollover function and a multiple key recognition,
the key encoder is provided with an integrated permanent-key-depression recognition.
The code of the key recognized is stored in a register, causing an interrupt to be released in the
internal interrupt controller.
Connectors X0 to X1 for columns and connectors Y0 to Y2 for lines are used for the heparin
pump.
Two external interrupt inputs
Connectors EX0 to EX1 are provided as additional interrupt inputs. The respective interrupt is
released by a rising edge at the inputs.
The pulses of the optical sensor are converted into a digital signal by comparator IC 13 and
connected to input EX0.
A signal, which is reduced to 5 V, is applied to input EX1. This signal is emitted by the optical
detector in the hemodialysis machine. This signal is a square-wave oscillation of approx. 100 Hz
with air or a clear fluid being recognized by the sensor; with blood, L level is applied to the signal.
Interrupt controller
In addition to the interrupts released by the key encoder and the external interrupt inputs, a 1-MS
and a 16-MS interrupt is made available by the gate array.
All interrupts can be individually inhibited or released in a corresponding control register.
After an interrupt request, the releasing interrupt must be determined in the respective routine by
reading the interrupt flag register. In order to erase the respective interrupt flag, it suffices to read
the pertinent address (see gate array data sheet).
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Fresenius Medical Care 4008 4/09.03 (TM)