Rev. 1.10
26
October 23, 2020
Rev. 1.10
27
October 23, 2020
BC66F5652
2.4GHz RF Transceiver A/D Flash MCU
BC66F5652
2.4GHz RF Transceiver A/D Flash MCU
System Architecture
A key factor in the high-performance features of the Holtek range of microcontrollers is attributed
to their internal system architecture. The device takes advantage of the usual features found within
RISC microcontrollers providing increased speed of operation and enhanced performance. The
pipelining scheme is implemented in such a way that instruction fetching and instruction execution
are overlapped, hence instructions are effectively executed in one or two cycles for most of the
standard or extended instructions respectively. The exceptions to these are branch or call instructions
which need one more cycle. An 8-bit wide ALU is used in practically all instruction set operations,
which carries out arithmetic operations, logic operations, rotation, increment, decrement, branch
decisions, etc. The internal data path is simplified by moving data through the Accumulator and
the ALU. Certain internal registers are implemented in the Data Memory and can be directly
or indirectly addressed. The simple addressing methods of these registers along with additional
architectural features ensure that a minimum of external components is required to provide a
functional I/O and A/D control system with maximum reliability and flexibility. This makes the
device suitable for low-cost, high-volume production for controller applications.
Clocking and Pipelining
The main system clock, derived from either an HXT, LXT, HIRC or LIRC oscillator is subdivided
into four internally generated non-overlapping clocks, T1~T4. The Program Counter is incremented
at the beginning of the T1 clock during which time a new instruction is fetched. The remaining
T2~T4 clocks carry out the decoding and execution functions. In this way, one T1~T4 clock
cycle forms one instruction cycle. Although the fetching and execution of instructions takes place
in consecutive instruction cycles, the pipelining structure of the microcontroller ensures that
instructions are effectively executed in one instruction cycle. The exception to this are instructions
where the contents of the Program Counter are changed, such as subroutine calls or jumps, in which
case the instruction will take one more instruction cycle to execute.
For instructions involving branches, such as jump or call instructions, two machine cycles are
required to complete instruction execution. An extra cycle is required as the program takes one
cycle to first obtain the actual jump or call address and then another cycle to actually execute the
branch. The requirement for this extra cycle should be taken into account by programmers in timing
sensitive applications.
Fetch Inst. (PC)
(System Clock)
f
SYS
Phase Clock T1
Phase Clock T2
Phase Clock T3
Phase Clock T4
Program Counter
PC
PC+1
PC+2
Pipelining
Execute Inst. (PC-1)
Fetch Inst. (PC+1)
Execute Inst. (PC)
Fetch Inst. (PC+2)
Execute Inst. (PC+1)
System Clocking and Pipelining