The Infineon SAB80C535 has 6 BiDirectional 8-bit ports and one Input only 8-bit port. The part is used with external code memory so most modern day replacements will end up being different with on-board Flash for code.

If the existing design used a big bank of XDATA RAM you'll have to select a part that supports an external memory bus.

The 80C535 has an enhanced design of the TIMER 2 and if you used the additional three capture / compare registers you may find it difficult to find equivalent functionality on other 8051 type parts. It may be possible to adapt to another part and make use of a PCA to gain similar functionality. A lot depends upon the existing MCU usage in your existing applications.

The 'C535 does have an 8-bit A/D capability. It should be easy to find equivalent or better functionality on other parts.

Another feature of the 'C535 is a hardware watchdog timer which is available on many other parts these days.

Contrary to what Erik may have recalled, the 'C535 does not (in its data sheet) have any hardware I² support. So this makes the decision of where to look for a replacement a bit simpler.

I would follow Erik's recommendation to take a close look at the SiLabs part families. From seeing the overall architecture of the 'C535 part I think you could look at the C8051F02x, C8051F04x, C8051F06x, C8051F12x and C8051F13x series parts from SiLabs. Do note that SiLabs parts are 3.3V parts with 5V tolerant I/Os but may require some design retrofit if your current platform was a 5V design. Note that also you are looking at the 100-pin packages to get the 8 port I/O. A huge advantage is the on-board debug capability including hardware breakpoints accessed via the USB debug pod that makes development much easier than the ICE type box that you may have used with the 80C535.

Michael Karas