TimeKeeper and ZeroPower RAMs          Jed Margolin
Original:  7 October 1996
Revised: 6 January 2001, 21 November 2025


Where Used:

 

Hard Drivin', Race Drivin', and Steel Talons use both a M48Z02-150 ZeroPower RAM and a 48T02-150 TimeKeeper RAM.

 

Why Should I Care?:

 

In Hard Drivin' and Race Drivin' these parts are used to store the high score table, game settings, and control settings. The TimeKeeper is used to produce a table showing games played by hour and day.

 

The control setting are stored in the TimeKeeper SRAM. When the part fails you must set up the controls each time you power-up the game. This is a real pain.

 

Options:

 

1. Live with it.

 

2. Don't turn the game off.

 

3. Isolate VCC for the TimeKeeper and Zeropower RAMs from the game +5V with a 1N5817, connect it to a separate 4.0V power supply through another 1N5817, and leave the 4.0V power supply on all the time.

 

4. Buy a new part. As of November 2025 Mouser still has them but they are expensive. (Buy the 150 ns parts.)

 

5. Fix the old part by installing a new battery (Not For the Fainthearted!)

 

If you have a Race Drivin' game, and assuming the TimeKeeper goes first, you may be able to buy time by swapping the TimeKeeper on the Main Board with one of the ZeroPower RAMs on the DSK Board.

 

If you choose option 1-4 there is no need to read any further. If you choose option 5, prepare for a small adventure.
 

 

History of the Parts:

 

Both parts were originally made by Mostek. Mostek was acquired by SGS-ATES, which was then acquired by Thomson CSF which changed its name to SGS-Thomson and was then spun out as ST Microelectronics.

 

For the M48Z02 datasheet Click Here. For the M48T02 datasheet Click Here.

 

 

What They Are:

 

The 48Z02-150 ZeroPower RAM is a 2Kx8 static RAM (150ns) with power control circuitry and a built-in 3.3V lithium battery. When the power control circuitry detects VCC lower than 4.5V, it disables writes to the RAM. When VCC drops below 3.3V it switches to the built-in battery.

 

The RAM and power control circuitry are in a standard plastic IC package; the battery is encapsulated in what SGS-Thomson calls a 'CAPHAT' which lays over the IC part and attaches to it at the ends. There are two pins that stick up from the top of the IC part between pins 12 and 13 and connect to the battery in the CAPHAT. These pins are not accessible and the battery is not intended to be user replaceable.

 

The 48T02-150 TimeKeeper RAM is similar to the 48Z02 ZeroPower RAM, but it also contains a clock/calender. The CAPHAT contains a 32.768 KHz crystal in addition to the lithium battery. The crystal is connected to the IC part by two pins that stick up from the top of the IC part between pins 1 and 24. These pins are also not accessible.
 

 

Why I Used Them:

 

The advantages of these parts is that writes are done at full speed (150ns) and the life of the part is not affected by the number of writes performed.

 

This is as opposed to EEPROMs where writes take considerably longer (on the order of 4ms) and the parts are only rated for a maximum number of writes (originally 10K, but currently more like 100K).

 

The lifetime for the TimeKeeper and ZeroPower RAMs is determined by the lifetime of the battery.
 

 

Battery Lifetime:

 

When I first started using them, in 1984, the data sheets contained charts that related battery lifetime to both temperature and the amount of time the part operated from the battery. Unfortunately, I no longer have the original data sheets, but according to my calculations at the time:

 

   " For a game powered up 50% of the time, in an ambient of 75 degrees
      Fahrenheit, the Lithium Battery can be expected to last for 6 years. (99%
      will still be working.) After 8 years about 50% can be expected to still work."

 

This applies only to the ZeroPower RAM. The TimeKeeper draws more current because of the clock/calendar. For this reason the clock/calendar can be turned off to preserve battery life. This can be done in Self-Test in the screen used to set the time.

 

The current data sheet simply states that the battery (for both ZeroPower and TimeKeeper):

 

   " has sufficient capacity and storage life to maintain data and clock functionality
     for an accumulated time period of at least 10 years in the absence of power
     over the operating temperature range."

 

The Ambient Operating Temperature is given as 0 - 70 degrees Celcius.

 

(At higher temperatures the IC current leakage increases but so does the battery capacity. At lower temperatures the IC current leakage decreases, as does the battery capacity.)

 

The 10 year specification appears to be an improvement over the original specs and may be the result of:

 

   1. a better, lower current design;

 

   2. better batteries than were available in 1984;

 

   3. the Marketing Department.
 

 

OK, How Do I replace the Battery?

 

First some warnings are in order.

 

Lithium batteries can be dangerous if handled improperly.

 

  1. Do Not Cut it open.

 

  2. Do Not Eat it.

 

  3. Do Not Throw it in a fire, it will probably explode.

 

  4. Do Not Short it out, it will probably explode.

 

  5. Do Not Get it too hot, it will probably explode.

 

Now, about replacing the battery in a TimeKeeper.

 

The following is based on a TimeKeeper with a date code of 1988. If you have a more recent part, your mileage may vary.

 

The battery and the 32.768 KHz crystal are in the CAPHAT. They are encapsulated together with epoxy which cannot be melted. However, the remainder of the CAPHAT uses a thermoplastic material which *can* be melted. In fact, it can be melted with a soldering iron. (The IC part uses a thermoset plastic which cannot be remelted.)

 

The battery (a small lithium coin-type) is located in the end near pins 12 and 13, and takes up about half of the CAPHAT.

 

The crystal (about the size of a lithium coin-type battery) is located in the end near pins 1 and 24, and takes up the other half of the CAPHAT.
 


 
Using a soldering iron, start at the pin 12 end of the package and start melting the CAPHAT until you have exposed the battery. Be especially careful around the pins where the battery connects to the IC part. They stick up from the top of the IC part between pins 12 and 13.

 

Once you have removed enough plastic you need to break the epoxy between the battery and the crystal. I used a Dremel with a cutting disc.

 

A suggestion: The melting plastic can be nasty. Work in a well ventilated area. Outdoors would be nice.

 

Another suggestion: If you put the TimeKeeper in a IC socket you can work on it without worrying about bending the IC pins.

 

Once you have exposed the battery, carefully remove it.

 

If you damage the crystal, or want to use a humongous battery, you will need to remove the crystal as well. That's what I did on my first one.

 

I replaced the crystal with a small cylindrical crystal (32.768 KHz) from JDR Microdevices [now gone]. For the battery I used a BR-2325 3V Lithium Coin-type cell, also from JDR. (Radio Shack sells a variety of lithium cells, including small ones that make it unnecessary to remove the crystal.) You can get crystals and Lithium coin cells on eBay.

 

The battery I used was so large it took up the entire space on top of the IC part, so I hung the crystal off the front. (The Main Board accommodates this with no problem.)
 


 

You need to attach the battery so it doesn't fall off. But you also need to be able to remove it when it eventually needs to be replaced. (So don't use epoxy.)

 

You also need to protect it against condensation which will create a leakage path and cause the battery to expire prematurely.

 

The following is what I did.

 

Warning: Be especially careful when you work with the Battery. The Battery is alive. Don't short it out.

 

When I did this in 1996 I soldered wires to the Lithium Coin cell. It turns out that soldering to a Lithium cell is a really bad idea.

 

I have recently (2025) had to replace Lithium coin cells in other devices (the DS3231 Real-Time-Clocks and NEO7M GPS modules).

 

The easiest way is to use a battery holder.

 

This is one that I got from AliExpress at https://www.aliexpress.us/item/3256804661300685.html

 

 

 

The other way is to use a spot welder to attach a thin tin strip to the battery.  I got this one at AliExpress at https://www.aliexpress.us/item/3256806541240211.html

 

 

I have only done a few so far but it works.

 

This is a CR2032 that I did recently (2025). You can probably do better.

 

 

 

 

 

The Spot Welder comes with a small roll of tin which you can cut with scissors.

 

It is important to keep the tips clean. To clean them I use 0000 steel wool which you can get at Home Depot (if you are in the US). https://www.homedepot.com/p/Homax-Super-Fine-Grit-Steel-Wool-12-Pad-10120000-6/306606236  

 

It is also the best way to clean the tip of a soldering iron.

 

Make sure the spot welder is turned OFF before you clean the tips.

 

 

You should be able to mount the new coin cell on the top of the IC with a piece of double-sticky foam tape.

 

From 1996:

 

I used clear nail polish to coat the crystal connections and the battery connections. I also coated the perimeter of the battery. By this I mean the space between the  positive case and the negative inner disk.)

 

I liberally applied RTV (silcone rubber-in-a-tube) over the top of the battery and IC part. This is to help keep the battery in place so it doesn't fall off if the double-sticky tape gives way.

In 2025 I think it is still a good idea. 

 

In my second TimeKeeper I removed only the battery, being careful not to damage the crystal. The replacement battery I used was a CR-1220, mounting it in the manner already described.

 

Note: the first two numbers in the lithium coin-cell designation appears to be the diameter in millimeters. The BR-2325 is 23 mm (0.905") in diameter;  the BR-1220 is 12 mm (0.472") in diameter.

 

The above spot welder is only good for large coin cells like the CR2032 and CR1620.

 

For smaller coin cells like the CR927 I am buying one that looks like this:

 

 

I only just ordered it so I can’t vouch for it. I am getting it on eBay at https://www.ebay.com/itm/127430217008

 

 

Happy spot welding.

 

 

Jed Margolin