Hello Thomas,
Instead of wasting your time with the 1232(DS,MAX etc) I suggest you the MCP810(or LM810 or ADM810 etc)with the P89C51RD2 devices. This is what I am doing with the new products, though I have not field tested this combination.

I have used the DS1232 variants with the 89C51/52 Atmel, series and manufactured hundreds of them without any problems.

As Erik suggested connect a 4K7 resistor between the MCP810 and the RESET pin the P89C51RD2, connect this RESET pin, TXD, RXD, GND, VCC to six pin berg stick(female), you then have a neat compact ISP header. You can also make an adapter according to schematic provided by ESA (FlashMagic).This makes an excellent development system.

You will lose the fun of ISP if you are trying to use the 1232 with RD2.

You easily design a PUSH BUTTON reset without the DS1232.

Another news: you make not even require an external brown out since the new devices from Philips the P89V51RD2 series has built in brown out, this chip is already available in Chennai, and it seems that the BN series may not be available any more.


Regards,
John.