Fresenius Medical Care 4008 E Technical Manual page 351

BUS logic
In conjunction with the signals -DEN, DT/-R and ALE, three TTL latches (74HC573) and a data
bus driver (74HC245) assume the task of editing the multiplexed data-address bus.
The address bus is fully decoded and provided with a physical address range of 1 MByte.
The edited data and address bus is conducted to the internal peripheral modules of CPU1 and to
the 64-pin contact strip.
The chip-select signals for external input/output boards are edited by the programmable storage
and peripheral equipment chip-select logic incorporated in the microcontroller.
EPROM
The program to be performed by the machine is programmed in the EPROM. The 32-pin EPROM
base can be equipped with program memory EPROMs of a size of up to 512 kBytes. The CS line
of the EPROM is connected to the -UCS (Upper Memory Chip Select) signal of the microcontrol-
ler.
This output of the microcontroller becomes active as soon as the microcontroller reads a program
code or table data out of the EPROM.
The scope of range, within which this line is intended to be active, can be programmed.
Static RAM
During operation of the machine, the 128-kByte read-write memories installed on the P.C.B. are
used as data memories for temporary data, tables and branch vectors.
The CS line of the RAM is connected to the _LCS (Lower Memory Chip Select) signal of the
microcontroller.
This output of the mcirocontroller becomes active, if the microcontroller requires or intends to
store RAM data. The direction of data transfer is determined in conjunction with the -RD and -WR
signals.
The scope of the range, within which this line is intended to be active, can be programmed.
Nonvolatile RAM
The 48Z02 nonvolatile read-write memory (2 kBytes, no more than 8 kBytes) is provided for
storing important data, which shall remain preserved after the machine has been switched off.
A battery incorporated in the nonvolatile RAM as well as a voltage-monitoring circuit guarantee
that the RAM cells are supplied with voltage and, consequently, that the data is preserved after
the machine has been switched off.
The following data is stored in the nonvolatile RAM:
– Calibration data
– Operating parameters
– Data for power failure protection
The CS line of the NOVRAM is connected to the -MCS0 (Midrange Memory Chip Select 0) signal
of the microcontroller.
This output of the microcontroller becomes active, if the microcontroller requires or intends to
store NOVRAM data. The direction of the data transfer is determined in conjunction with the -RD
and -WR signals.
The scope of the range, within which this line is intended to be active, can be programmed.
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Fresenius Medical Care 4008 4/09.03 (TM)