Похоже Вам не повезло с поддержкой симулятором Keil выбранного Вами ARM. Уж больно куцый список VTREG. Сравните:
dir vtreg TRAPS: ulong, value = 0x0000005F DBGCOMCR: ulong, value = 0x00000000 DBGCOMRD: ulong, value = 0x00000000 DBGCOMWR: ulong, value = 0x00000000 XTAL: ulong, value = 0x00B71B00 IRC: ulong, value = 0x003D0900 RTCX: ulong, value = 0x00008000 PLLIN: ulong, value = 0x00B71B00 HCLK: ulong, value = 0x112A8800 CCLK: ulong, value = 0x02DC6C00 USBCLK: ulong, value = 0x02DC6C00 V3: float, value = 3.29999995 PORT0: ulong, value = 0xFFFFFFFF PORT1: ulong, value = 0xFFFFFFFF PORT2: ulong, value = 0x00003FFF PORT3: ulong, value = 0x078000FF PORT4: ulong, value = 0xF300FFFF S0IN: ushort, value = 0xFFFF S0OUT: ushort, value = 0x0000 S0TIME: uchar, value = 0x01 S0BAUD: ulong, value = 0x00002580 S1IN: ushort, value = 0xFFFF S1OUT: ushort, value = 0x0000 S1TIME: uchar, value = 0x01 S1BAUD: ulong, value = 0x00002580 S2IN: ushort, value = 0xFFFF S2OUT: ushort, value = 0x0000 S2TIME: uchar, value = 0x01 S2BAUD: ulong, value = 0x00002580 S3IN: ushort, value = 0xFFFF S3OUT: ushort, value = 0x0000 S3TIME: uchar, value = 0x01 S3BAUD: ulong, value = 0x00002580 I2C0_IN: ushort, value = 0xFFFF I2C0_OUT: ushort, value = 0xFFFF I2C1_IN: ushort, value = 0xFFFF I2C1_OUT: ushort, value = 0xFFFF I2C2_IN: ushort, value = 0xFFFF I2C2_OUT: ushort, value = 0xFFFF SPI_IN: ushort, value = 0x0000 SPI_OUT: ushort, value = 0x0000 SSP0_IN: ushort, value = 0x0000 SSP0_OUT: ushort, value = 0x0000 SSP1_IN: ushort, value = 0x0000 SSP1_OUT: ushort, value = 0x0000 VREF: float, value = 3.29999995 AD00: float, value = 0 AD01: float, value = 0 AD02: float, value = 0 AD03: float, value = 0 AD04: float, value = 0 AD05: float, value = 0 AD06: float, value = 0 AD07: float, value = 0 AOUT: float, value = 0 CAN1ID: ulong, value = 0x00000000 CAN1L: uchar, value = 0x00 CAN1B0: uchar, value = 0x00 CAN1B1: uchar, value = 0x00 CAN1B2: uchar, value = 0x00 CAN1B3: uchar, value = 0x00 CAN1B4: uchar, value = 0x00 CAN1B5: uchar, value = 0x00 CAN1B6: uchar, value = 0x00 CAN1B7: uchar, value = 0x00 CAN1IN: ushort, value = 0x0000 CAN1OUT: ushort, value = 0x0000 CAN2ID: ulong, value = 0x00000000 CAN2L: uchar, value = 0x00 CAN2B0: uchar, value = 0x00 CAN2B1: uchar, value = 0x00 CAN2B2: uchar, value = 0x00 CAN2B3: uchar, value = 0x00 CAN2B4: uchar, value = 0x00 CAN2B5: uchar, value = 0x00 CAN2B6: uchar, value = 0x00 CAN2B7: uchar, value = 0x00 CAN2IN: ushort, value = 0x0000 CAN2OUT: ushort, value = 0x0000 DCC_SIN: ushort, value = 0xFFFF DCC_SOUT: ushort, value = 0x0000 DCC_TIME: uchar, value = 0x01