1.1.3. Additional Features
The C8051F04x MCU family includes several key enhancements to the CIP-51 core and peripherals to
improve overall performance and ease of use in end applications.
The extended interrupt handler provides 20 interrupt sources into the CIP-51 (as opposed to 7 for the stan-
dard 8051), allowing the numerous analog and digital peripherals to interrupt the controller. An interrupt
driven system requires less intervention by the MCU, giving it more effective throughput. The extra inter-
rupt sources are very useful when building multi-tasking, real-time systems.
There are up to seven reset sources for the MCU: an on-board VDD monitor, a Watchdog Timer, a missing
clock detector, a voltage level detection from Comparator0, a forced software reset, the CNVSTR0 input
pin, and the /RST pin. The /RST pin is bi-directional, accommodating an external reset, or allowing the
internally generated POR to be output on the /RST pin. Each reset source except for the VDD monitor and
Reset Input pin may be disabled by the user in software; the VDD monitor is enabled/disabled via the
MONEN pin. The Watchdog Timer may be permanently enabled in software after a power-on reset during
The MCU has an internal, stand alone clock generator which is used by default as the system clock after
any reset. If desired, the clock source may be switched on the fly to the external oscillator, which can use a
crystal, ceramic resonator, capacitor, RC, or external clock source to generate the system clock. This can
be extremely useful in low power applications, allowing the MCU to run from a slow (power saving) exter-
nal crystal source, while periodically switching to the fast (up to 25 MHz) internal oscillator as needed.
Figure 1.6. On-Board Clock and Reset