Apparatus for connecting electronic modules containing integrated circuits and backup batteries

Apparatus for connecting a data storage module to an external circuit. A power supply terminal is connected between the module and the external circiut before signal terminals are connected. Apparatus includes a printed circuit board male card edge connector having selected card edge pins that extend farther than other card edge pins.

TECHNICAL FIELD 
This invention relates to integrated circuits with power backup batteries 
and more particularly to electrical connection apparatus and methods for 
modules containing the integrated circuits and backup batteries. 
BACKGROUND OF THE INVENTION 
Semiconductor memories, as first developed, were inherently volatile (i.e., 
would not retain the stored data if power was removed), and various 
methods have been developed to either make the devices nonvolatile or to 
add backup batteries to the circuitry attached to the integrated circuit. 
In particular, one method of adding backup batteries has been to package 
one or two lithium batteries in the same housing with an otherwise 
volatile semiconductor memory to make the memory operate as a nonvolatile 
memory. Small lithium batteries have been developed in the last few years, 
and accelerated life tests have indicated that, under a relatively light 
electrical load, the battery should provide voltage sufficient to retain 
data in a semiconductor memory for well over ten years if the battery is 
operated at room temperature. 
Such nonvolatile data storage makes it possible to utilize a transportable 
electronic data storage module which can be connected to an external 
circuit and be written into, be disconnected from the external circuit 
with no power applied to the module, and later be reconnected to the same 
or another external circuit, and have its data read out. 
However, it has been discovered that this process is unreliable in that 
some of the data is lost on an intermittent basis, and also, at times, the 
life of the lithium batteries has been severely shortened. 
It can therefore be appreciated that a method or apparatus to make this 
transportable data storage process reliable and which also prevents severe 
degradation of the lithium batteries would be highly desirable. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a means of reliably 
utilizing a battery backed up semiconductor memory circuit in a 
transportable module. 
It is also an object of this invention to permit the use of battery backed 
up semiconductor memories in transportable modules without adversely 
affecting the life of the backup battery or batteries. 
As shown in an illustrative embodiment of the invention, a transportable 
module includes a volatile memory, a power backup battery, and a connector 
which is configured to make a connection with at least one of the external 
primary power supply voltages before any of the signal connections are 
made to the module. 
In a further aspect of the illustrative embodiment, the connector is 
preferably configured as a plurality of card edge pins comprising metallic 
traces on a portion of a printed circuit board inside the module, which 
card edge pins are arranged to be inserted into a female card edge 
connector of an external circuit, and which female card edge connector 
contains a like plurality of spring contacts which press against the metal 
traces to make electrical contact between the module and the external 
circuit. For connecting a power supply reference voltage from the external 
circuit to the module, at least one of the card edge pin metallic traces 
used for connecting the power supply reference voltage is fabricated to 
extend farther than the other traces such that the chosen trace makes 
contact with the spring contact in the female card edge connector before 
the other traces make contact with their respective spring contacts, 
thereby ensuring that a predetermined power supply reference voltage is 
applied to the module before signal connections are made between the 
module and the external circuit. 
Also described as an illustrative embodiment of the invention is a method 
for connecting an electronic module containing a backup battery to another 
circuit comprising the step of making at least one power supply reference 
voltage connection between the module and the other circuit prior to 
making any of the signal connections between the module and the other 
circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The failure described in the Background of the Invention has been analyzed, 
but a completely definitive reason for the loss of data and the shortened 
life of the battery has not been determined. It is theorized, however, 
that the loss of data and degradation of the battery is caused by a 
transitory condition which intermittently occurs when the module is 
inserted into the female card edge connector of an external circuit. 
During this transitory condition, the backup battery is shorted or 
partially shorted, resulting in the loss of the backup supply voltage used 
to preserve the data in each of the volatile semiconductor memory cells, 
and thus, depending upon the amount and duration of the voltage loss, 
causing some if not all of the cells to lose their data. Also, the lithium 
battery is designed to provide a low amount of current for a relatively 
long period of time. This period of time, however, is severely shortened 
if the battery is shorted for even a brief period. Thus, the malfunctions 
described are consistent with a temporary short or low impedance across 
the battery. 
The exact mechanism causing the short has not been identified. Included in 
the module is a voltage controller circuit which is fabricated with CMOS 
integrated circuit processing technology wherein P-type wells are disposed 
in an N-type substrate. N-channel transistors are disposed in the P-type 
wells and P-channel transistors are disposed in the N-type substrate. The 
negative terminal of the lithium backup battery is connected to P-type 
wells and is defined as being the ground terminal of the module. The 
positive terminal of the battery is connected to a switching circuit of 
the CMOS integrated circuit which in turn couples the backup supply 
voltage to the memory cells during the time that the primary power supply 
voltage is not applied to the module. The memory cells can be embodied 
either in one or more separate integrated circuits or in the same 
integrated circuit as the voltage controller circuit. 
It is believed that a bipolar transistor action is created in the voltage 
controller CMOS integrated circuit by the application of external signal 
voltages from the external circuitry to signal inputs and/or outputs of 
the CMOS integrated circuit prior to making connection to the CMOS 
integrated circuit of any of the external primary power supply voltages. 
This transistor action would, according to this theory, cause a short or 
low impedance across the battery. 
Although the exact cause of the failure mechanism has not been identified, 
the failure has been eliminated by controlling the connection and 
disconnection sequence of a primary supply voltage terminal with respect 
to the signal terminals. As shown in the sole FIGURE a module 10 includes 
a printed circuit board 12 housed in a plastic case 14. Mounted on the 
printed circuit board 10 are a static random access memory integrated 
circuit 16, a CMOS voltage controller integrated circuit 18, and a lithium 
power backup battery 20. The integrated circuit 16 may consist, for 
example, of a 16K.times.8 memory integrated circuit such as part number 
TC5564PL-15 manufactured by Toshiba. The integrated circuit 18 may 
consist, for example, of a Nonvolatile Controller/Decoder integrated 
circuit such as part number DS1221 manufactured by Dallas Semiconductor 
Corporation. The lithium power backup battery 20 may consist, for example, 
of a 3 volt battery such as part number BR2325 manufactured by Ray-O-Vac. 
The integrated circuit 18 compares the incoming primary power supply 
voltage (which should typically be at +5.0 volts, plus or minus 5 percent) 
to the backup battery voltage, and couples whichever voltage is of greater 
value to the VCC power supply terminal of the memory integrated circuit 
16. 
Also shown in the sole FIGURE as an extension of the printed circuit board 
12 is a connector 22. The connector 22 is accessible from an opening in 
the plastic case 14 and consists of a plurality of metallic connection 
traces 24 which are typically wider than a number of conventional 
interconnection traces 26 on the printed circuit board 12 which provide 
interconnections between the integrated circuits 16 and 18, the power 
backup battery 20, and the connector 22. The metallic traces 24 are 
conventionally referred to as card edge pins and are dimensioned to mate 
with a female card edge connector 28 which contains a like plurality of 
spring contacts 30. It will be understood that attached to, and in 
electrical contact with, the card edge connector 28 is a separate external 
circuit 29 partially shown in the sole FIGURE. The external circuit 29 
provides power supply voltages to the module 10 and transfers information 
to and from the module 10 via electrical signals. In the preferred 
embodiment shown, the connector 22 has metallic connection traces on both 
sides of the printed circuit board 12; and, the card edge connector 28 has 
spring contacts for making electrical connections to the metallic 
connection traces on both sides of the connector 22. 
Of special significance to the present invention is the length of the 
metallic connection traces 24 on the connector 22. Specifically, the 
metallic connection traces for connecting the power supply voltages to the 
module 10, shown as metallic connection traces 32 and 34, are more 
extended than the metallic interconnecting traces used to connect 
electrical signals to and/or from the module 10. The trace 32 connects the 
primary power supply ground reference voltage (GND) to the module 10, and 
the trace 34 connects the primary power supply postive voltage terminal 
(VCC) to the module 10. In the preferred embodiment the spring contacts 30 
of the card edge connector 28 are all of equal length. 
In operation, when the module 10 is inserted into the card edge connector 
28, the metallic connection traces 32 and 34 make physical and electrical 
contact with their respective spring contacts 30 before the other metallic 
connection traces are contacted. Similarly, when the module 10 is 
disconnected from the card edge connector 28, the metallic connection 
traces 32 and 34 remain in electrical contact with their respective spring 
contacts 30 after the other metallic connection traces have been 
disconnected from their respective spring contacts. In this manner the 
electrical signal voltages are never connected between the module 10 and 
the external circuit 29 unless the power supply voltages are also 
connected. Tests have shown that the aforementioned problems of data loss 
and shortened battery life are obviated by the use of the embodiment just 
described. 
Testing has also shown that making only the metallic trace associated with 
the primary power supply ground reference voltage extend more than the 
other metallic traces is sufficient to prevent the problems of data loss 
and shortened battery life. Likewise, testing has further shown that 
making only the metallic trace associated with the primary power supply 
positive voltage terminal extend more than the other metallic traces is 
also sufficient. 
Although the invention has been described in part by making detailed 
reference to a certain specific embodiment, such detail is intended to be 
and will be understood to be instructive rather than restrictive. It will 
be appreciated by those skilled in the art that many variations may be 
made in the structure and mode of operation without departing from the 
spirit and scope of the invention disclosed in the teachings contained 
herein. For example, other connection apparatus can be used with the 
present invention. Moreover, electrical circuitry could be included in 
either the module or the external circuit which would prevent application 
of electrical signals to the integrated circuits of the module either 
until after one or more primary power supply voltage connections are made 
to the module.