Fresenius Medical Care 4008 E Technical Manual page 364

Microcontroller system (circuit diagram 4/6)
Microcontroller 80C535 (IC 12) is used as CPU. The microcontroller is provided with a multiplex-
ed 8-bit data and address bus as well as freely available ports. The clock pulse frequency of the
processor is deducted from a 11.0592-MHz crystal oscillator. A serial interface (TxD/pin 22 and
RxD/pin 21) is directly made available by CPU 80C535. This interface is used for the communica-
tion between CPU 2 and CPU 1 (P.C.B. LP 631).
The peripheral module PSD313 (Programmable System Devices) contains all elements necessa-
ry for the microcontroller system. The interface to the microcontroller consists of the multiplexed
8-bit bus and address lines A8 to A15 mentioned above, as well as of the following control lines
/RD-, /WR-, ALE-, /PSEN- and /RST. A further element of the PSD313 is represented by the 128-
Kbyte EPROM (read only memory), where the program is filed, as well as a 2-Kbyte SRAM, which
is used by the microcontroller. In addition, the module contains a programmable logic (PLD) for
the generation of the necessary chip-select signals, which are emitted at ports B and C, and an
address latch, which is available via port A. This address latch serves to separate data signals
(D0 to D7) and address signals (A0 to A7) and/or to store the address bytes.
Tasks of the control lines:
/RD ReaD
/WR WRite
ALE AddressLatchEnable Storing of the address bytes A0 to A7 into the latch
/PSEN ProgramStorENable
/RST ReSeT
The storage module MK48Z08 (IC 13) constitutes an 8-Kbyte NOVRAM (nonvolatile read access
memory). This NOVRAM is required for protecting the calibration data. A part of the NOVRAM,
which is not needed for the calibration data, is used as normal RAM during the program run.
Reading of the addressed RAM point
Writing into the addressed RAM point
Reading of operations/commands from the EPROM
Microcontroller defined at zero address or new system start
Fresenius Medical Care 4008 4/09.03 (TM)
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