Note: Descriptions are shown in the official language in which they were submitted.
2Q709~
Method and apparatus for controlling writing to memory
The invention relates to a method for control-
ling writing to a memory, in which method a memory write
operation is permitted only within a predetermined time
interval from the writing of a predetermined key code
to a predetermined memory location.
Random-access memory (RAM) is a semiconductor
memory to which information can be rapidly stored,
wherefore RAM is used in microcomputers when rapid
storing or reading of information is required. On the
other hand, it is also characteristic of RAM that the
information written into it is erased when supply
voltage is shut off. However, the types of RAM that
require only a little power to store information can be
used to store information even during a power failure
if they are provided with a standby power supply, e.g.
a battery or an accumulator.
In a slot machine RAM can be used, for example,
for storing information on money and failures. This
information is important for the operation of the whole
machine, since without reliable information the opera-
tion of the machine can stop. The same information can
be stored simultaneously in several different memory
circuits so that when a failure occurs, the operation
can be continued with proper information. When several
memory circuits are used, the likelihood that the same
information would be erroneously treated reduces if an
interrupted writing operation is considered to have
caused the error.
In a known solution, unintentional alteration
of RAM contents is prevented by keeping one of the
signals controlling the memory write operation in a
state preventing writing to a memory. In this known
solution, a so-called chip enable signal CE is used for
: . ~
, , .,. . , ~ . ,; , ~ , ~., .. - , , :
: -, . . ~ . . .: .,
. . . , : , . ~, .,
,
~ 2~70986
this purpose in such a manner that the CE signal can be
activated only by such memory write sequences addressed
to RAM that are written within a fixed interval of time
from the writing of a key code word to a memory location
outside the RAM storage space. Thus, the likelihood that
the right code word is inadvertently given to the right
memory location and erroneous writing to RAM takes place
is extremely small.
When the information is secured by copying the
memory contents to another memory circuit, functioning
as a so-called backup memory, the copying rate is of
great significance: the supply voltage of the apparatus
may be shut off any time, and the copying may be left
uncompleted. However, the faster the copying can be per-
formed, the smaller is the likelihood that the copying
would be left uncompleted and fail.
The object of the present invention is to
provide a memory control ena~ling more rapid writing to
a memory.
This object is achieved by a method of the type
described in the introductory portion, said method being
characterized in that after a successful memory write
operation following the writing of each key code, a new
memory write operation is permitted within a predeter-
mined time interval from the previous one without re-
writing of the key code.
In the invention, a property which enables a
new write operation is connected with the giving of a
key code: after each successful write operation to RAM,
memory protection permits a new write operation without
a new key code within a fixed time interval. In other
words, if the first write operation is correctly per-
formed, the following write operation can be performed
without separate opening of the time window by a key
code. Time control is, however, maintained in the inven-
~ ~Q7~98~
tion. Due to the invention, a long data block can be
written to RAM as rapidly as the apparatus controlling
the memory can - provided, however, that there is not
too long a pause between the write operations - without
the time consuming operation of giving the key code in
connection with each write operation.
A further object of the invention is an
apparatus for controlling writing to a memory, compris-
ing control means for forming a memory activation signal
in response to the applying of a predetermined key code
to the control means, the control means comprising timer
means which are started by applying the key code and
which prevent the formation of the memory activation
signal when a predetermined time has elapsed since the
applying of the key code. The apparatus is characterized
in that the control means further comprise means for
restarting the timer means within a predetermined time
interval from the applying of the key code or the
previous memory write operation as a result of a
performed memory write operation.
Still another object of the invention is the
use o the apparatus accordin~ to the invention in a
slot machine for copying cash and operation data from
one memory to another for backup storage of the data.
In the following the invention will be
described, by way of example, in greater detail by means
of an embodiment with reference to the attached drawing.
The figure shows an embodiment of the inven-
tion, which generates one of the signals, in this case
a chip enable signal CE. The signal CE can control a
memory formed by one or several memory circuits.
; The circuitry shown in the figure generates the
chip enable signal CE for both read and write opera-
tions.
',
2Q7~98~
Information can be read without restrictions
from a semiconductor RAM: when the storage space con-
trolled by the circuitry is addressed for a RAM memory
read operation, a decoder circuit 4 sets its output
signal RAMREAD in an active state or 0, whereby an out-
put signal of an AND gate 8, i.e. the chip enable signal
CE, also changes to its active state 0, activating the
memory.
Writing to RAM is, however, protected accord-
ing to the invention.
Writing to the memory is started by addressing
a RAM enable register 1 located in a memory location
outside the RAM memory space to be written into and
writing a key code word of at least two bits, preferably
eight bits, to the register. The correct key code word
activates an output signal RAMOK of the enable register
1 by setting it in state 0. The signal RAMOK is passed
by an AND gate 5 to a time control timer 2, which sets
its output signal TIMEOK in an active state O and starts
to count the time interval. The TIMEOK signal is fed to
a second input of an OR gate 7.
A signal RAMWR is fed to the second input of
the OR gate 7 from a decoder circuit 3, which sets the
signal RAMWR in an active state 0 when the RAM memorv
space controlled by the circuitry is addressed for RAM
memory write. If a write operation is performed within
a certain time interval, i.e. when the signal TIMEOK is
0, the output of the OR gate 7 changes its state to
active or 0 and thereby activates even the signal CE.
If a write operation is not performed within
the given time interval, the time control timer 2 forces
the signal TIMEOK to assume a state 1, which prevents
the activation of the output of the OR gate 7 and there-
by the activation of the signal CE, even though RAMWR
would activate as a result of a write attempt.
2Q~9~6
The signals RAMWR and TIMEOK are also app'ied
to the inputs of an OR gate 6. The output of the OR gate
6 is connected to an input of an AND gate 5, another
input of which receives the signal RAMOK.
'; If a write operation is performed within the
given time interval, i.e. when the signal TIMEOK is in
state 0, both of the inputs of the OR gate 6 are simul-
taneously in state 0, which activates the output of the
gate 6 and resets the timer 2 through the AND gate 5.
It is then again possible, within the given time
interval, to perform a new write operation, which again
resets the timer 2. If a read operation is not performed
within the time interval and the signal TIMEOK changes
its state, the setting of the timer 2 through the OR
gate 6 is prevented. In this case, a write operation can
be performed only by rewriting the key code word to the
register 1.
The invention is particularly suitable for a
system which is provided with at least two RAM circuits
for storing inormation and in which one RAM circuit
is used for copying the information in the other RAM
circuit(s). The information to be stored is thereby
copied as blocks from a memory circuit to another.
Several memory circuit write operations are used for the
copying of each block. According to the invention, it
is necessary to write a key code word of at least two
bits to an external register in order that copying might
be started. There must not be a delay exceeding the
given time interval between the instants of writing two
pieces of information to be copied subsequently, or
otherwise the key code word must be given again. The
time interval is the time required for the control
apparatus to read information out of one memory circuit
- and to write information into another memory circuit
plus the time taken by the additional measures needed
~: :
.
~ .
.. . ,.. , ...... . ,.. ~. . .. : . . -
2 ~ 8 ~ ~ :
in copying. In the preferred embodiment of the inven-
tion, the time interval is of the magnitude 5 ,um,
The invention is particularly well suitable for
use in the copying of cash and operation data in a slot
machine or the like.
The figure and the description pertaining
thereto are intended merely to illustrate the invention.
In its details the invention can vary within the scope
of the attached claims.
~;~
';
