OK.
We have 87C520 and our memory loader is also on the chip. It's 16KB EPROM (OTP).
A new data are transferred via UART to the application RAM.
We send only one command to load it to the FLASH, if transfer is finished.
In case of new project with different memory and different algorithm we add to the
on-chip loader only new programming algorithm and new SIO command to define
which type of memory is re-programmed.
Usage of DIP config. switches insted of new SIO command is other way of solving.

Vaclav