HT82A821R_07 HOLTEK [Holtek Semiconductor Inc], HT82A821R_07 Datasheet - Page 5

• Manufacturer Part Number: HT82A821R_07
• Description: USB Audio MCU
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

Functional Description
Execution Flow
The system clock for the micro-controller is from a crys-
tal oscillator. The system clock is internally divided into
four non-overlapping clocks. One instruction cycle con-
sists of four system clock cycles.
Instruction fetching and execution are pipelined in such
a way that a fetch takes an instruction cycle while de-
coding and execution takes the next instruction cycle.
However, the pipelining scheme causes each instruc-
tion to be effectively executed in a cycle. If an instruction
changes the program counter, two cycles are required to
complete the instruction.
Program Counter - PC
The program counter (PC) controls the sequence in
which the instructions stored in the program ROM are
executed and its contents specify a full range of pro-
gram memory.
After accessing a program memory word to fetch an in-
struction code, the contents of the program counter are
Note: *10~*0: Program counter bits
Rev. 1.10
Initial Reset
USB Interrupt
Timer/Event Counter 0 Overflow
Timer/Event Counter 1 Overflow
Skip
Loading PCL
Jump, Call Branch
Return from Subroutine
#10~#0: Instruction code bits
Mode
S10
#10
*10
*10
0
0
0
0
S9
#9
*9
*9
0
0
0
0
Program Counter
Execution Flow
S8
#8
*8
*8
0
0
0
0
5
@7
#7
S7
*7
0
0
0
0
incremented by one. The program counter then points to
the memory word containing the next instruction code.
When executing a jump instruction, conditional skip ex-
ecution, loading to the PCL register, performing a sub-
routine call or return from subroutine, initial reset,
internal interrupt, external interrupt or return from inter-
rupts, the PC manipulates the program transfer by load-
ing the address corresponding to each instruction.
The conditional skip is activated by instructions. Once
the condition is met, the next instruction, fetched during
the current instruction execution, is discarded and a
dummy cycle replaces it to get the proper instruction.
Otherwise proceed with the next instruction.
The lower byte of the program counter (PCL) is a read-
able and writeable register (06H). Moving data into the
PCL performs a short jump. The destination will be
within the current program ROM page.
When a control transfer takes place, an additional
dummy cycle is required.
S10~S0: Stack register bits
@7~@0: PCL bits
Program Counter+2
Program Counter
@6
S6
#6
*6
0
0
0
0
@5
S5
#5
*5
0
0
0
0
@4
#4
S4
*4
0
0
0
0
@3
S3
#3
*3
0
0
1
1
@2
S2
#2
*2
0
1
0
1
HT82A821R
June 29, 2007
@1
S1
#1
*1
0
0
0
0
@0
S0
#0
*0
0
0
0
0