The Web Site to Remember National Semiconductor's Series 32000 Family


The PC532 is an interesting story. Beginning of the 1990's some people tried to build a NS32532 based computer system. Finally they were successful. The number of systems build was quite low compared to industrial standards. But nevertheless around 150 boards were build and shiped to enthusiastic NS32000 fans. The operating system used was NetBSD version 1.5.3 at least.

I saw my first PC532 at the Vintage Computer Festival (VCFe) in 2003. Figure 1 shows the system.

Fig. 1. A PC532 at VCFe 2003.

Later I came into contact with another PC532 owner. Unfortunately his system is no longer functional. On the next photo you can see not only the board but some probes from an oscilloscope. I tried to bring it up again. But at the end I was not successful :-(

Fig. 2. A PC532 showing no sign of working.

It is difficult to measure something inside a computer with an oscilloscope. Obviously a logic analyzer is much more helpful. If the system does nothing during booting one can check some control signals after reset is released. In this case the CPU seems to make something wrong. Therefore I decided to exchange this chip.

Fig. 3. A view of the PC532 board.

To exchange the CPU I took the pcb out of the case. On top of the CPU you can see a fan. The owner of this PC532 told me that his system was running at 30 MHz and the CPU got hot. Therefore the fan was necessary. My own NS32532 is running at 25 MHz with a heat-sink only. Four serial ports are available with two UARTs from Signetics. The IC from Adaptec is a SCSI controller which was used for the HDD.

Fig. 4. A close up view of the heart of the PC532.

Figure 4 shows the NS32532 CPU, now the fan is removed, the NS32381 FPU and 8 Mbytes of partity protected DRAM. Surprisingly the CPU and FPU were 25 MHz rated devices. Clocking them with 30 MHz is 20 % overclocking and maybe something died inside one chip due to the permanent overload. As a first step I replaced the 60 MHz oscillator with a 50 MHz one. The oscillator is sitting below the NS32381 FPU.

Fig. 5. Trying to break out the NS32532 CPU.

This was very strange! I tried to get the CPU out of its socket but nothing helped. At least I build a special construction which you can see in figure 5. But I hesitated to apply as much force as I could. The board was already bending and damaging the board was not an option! At the end I packed everything together and gave the PC532 back. Unrepaired.


Some documents about the hardware of the PC532 are available. The schematics together with the PAL equations give a good overview of the design.

PC532 Schematics (PDF)

PC532 PAL Definition (PDF)

Next chapter: PC532E