Now I want to test the C8051F021 family.

There are some differences to the original 8051:


On the original 8051 all additional pin functions ANDed with the ports and so both can be used at any time.

On the original 8051 all additional pin functions are fixed on a pin regardless if others used or not.
So if I decide later to use RXD0,TXD0 as UART or general IO it has no influence on using e.g. an external interrupt.


This all is now untrue on the C8051F family, but why ???


E.g. why I can not use the TX0 pin as output, if only the UART receive function was needed ?

How can I send a break, if no longer the pin function of TXD0 is available.

If I not clearly know which pins must be act as ports or as other peripherals, I must add an inverse crossbar (jumper field) to rearrange the needed functions.

All these sounds really crazy.

Know anybody, the reason, why no longer the easy and comfortable ANDing can be used and this irrational crossbar was needed ?


I see only one solution, that I must select a bigger device and enable all potential needeed peripherals already at the beginning of the project.
And also if they are not needed finally I let them enabled and unconnected forewer.
And for sending a break I need a wired AND of TXD0 with a second IO-pin.


So the only "usage" of the crossbar seems wasting pins.


Peter