When running the Kiel compiler with a Cygnal C8051F006 system, I pulled down the peripherals menu and looked at the crossbar switch. A brief look at the first XBR0 register shows the SMB pins, the SPI pins, and the UART pins. And checking and unchecking these pins will get (for a value of 0x05) SDA on P0.2 and SCL on P0.3, with the TX and RX on P0.0 and P0.1. This is totally against both the Cygnal chart on page 104 of the c8051F0xx.pdf file, and the first example on page 4 of http://www.cygnal.com/appnotes/an001.pdf . It also goes against all experience we have had with this device. My concern is that this crossbar box may reflect how the compiler/cygnal uVision dll combo actually model the device. Please pass this error message to Keil. Sean