Why not just build up a board around a DS89C450? That has the full code space filled with ISP/IAP-programmable FLASH on the chip. Unless you need additional hardware, all you'll need is a PC with a serial port, and the serial port hardware for programming the MCU, as described in the User Manual.

The PC serial port is something you'll have to work out, but the MCU itself is exactly the same as the DS89C430, with the exception of on-chip program store capacity. The upper 32 kBytes are in-application-programmable, so you can use them exactly like an external EEPROM. MAXIM will probably be happy to send you a couple of free samples.

BTW, I often interchange an 11.0592 MHz oscillator with a common 33 MHz one. No firmware change is reqired, and I simply set the PC serial port to 57.6 k-baud. It even happily programs itself at that rate.

Maybe a little more definition of your problem would be helpful. If all you want is to build your own board, you can do that pretty easily.

It might be cheaper to buy an old, used PC that has the serial port(s) on it than to buy a truly functional USB-interfaced serial port adapter ... since you may have to buy several to get one that works properly.

RE