English -> Computer -> MODIFICATION -> Put FPU on -2000.07.12 Updated-

[ Put FPU on ]

Recently a favorite book of mine has been "DOPING MAC" (Bunka-sha, 1950 yen). It includes many articles written about how to upgrade the SE/30, LC and Color Classic so I find it very interesting. In this book Mr.Gabezing wrote about expanding memory:

"It's useless to do modifications such as upgrade of CPU to 68040 (with FPU) or increasing the system clock rate without basic modifications such as expanding memory."

I hit on. I was thinking my next step was clock-up but I should do basic tune-up first. I already used 36MB memory so I would load it with FPU.

CPU chip on LC475 is 68LC040 which is a 68040 microprocessor without FPU. To install an FPU you needs to change microprocessor itself. Thinking of increasing the clock rate to 40 MHz later, I wanted to buy one rated for 40 MHz operation, but it was too expensive. So I decided to search for a second-hand chip rated for 25 MHz. At Akihabara Electric Parts I found one for 5000 yen. Its P.N. was XC68040RC25B, indicating that it was rated for only 25 MHz, but I bought it with a heat sink, hoping that it would allow pushing the clock higher than the rated limit.


Changing microprocessor was easy. At first I removed the 68LC040, keeping it level and slowly lifting it with a thin slot screwdriver. Then I pushed the full 68040 into the socket, taking care that it was oriented in the correct direction, and attached the heat sink with adhesive tape. Silicon sealant or caulking would be a more permanent way to attach it, and also improves the transfer of heat from the microprocessor to the heat sink. The new configuration is shown below:

CPU 68020 68030 68LC040 68040
FPU none ---> ---> built-in
clock speed 16MHz 25MHz ---> --->
width of bus 16bit 32bit ---> --->
max memory 10MB 36MB ---> --->
real memory 4MB 8MB 36MB --->
HD capacity 100MB 160MB ---> --->

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