HT46R22/HT46C22
Rev. 1.10
6
October 2, 2002
1
1
1
2
( -
9
:
;
& (
9
5 :
2
9
<
:
;
& (
9
:
2
( -
9
<
:
;
& (
9
<
:
<
<
+
( %
! #
=
9
# ' ! + :
Execution flow
Functional Description
Execution flow
The system clock for the microcontroller is derived from
either a crystal or an RC oscillator. The system clock is
internally divided into four non-overlapping clocks. One
instruction cycle consists 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 effectively execute in a cycle. If an instruction
changestheprogramcounter,twocyclesarerequiredto
complete the instruction.
Program counter
PC
The program counter (PC) controls the sequence in
which the instructions stored in program ROM are exe-
cuted and its contents specify full range of program
memory.
After accessing a program memory word to fetch an in-
struction code, the contents of the program counter are in-
cremented by 1. The program counter then points to the
memory word containing the next instruction code.
When executing a jump instruction, conditional skip ex-
ecution, loading PCL register, subroutine call, initial re-
set, internal interrupt, external interrupt or return from
subroutine, the PC manipulates the program transfer by
loading 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 256 locations.
When a control transfer takes place, an additional
dummy cycle is required.
Mode
Program Counter
*10
*9
*8
*7
*6
*5
*4
*3
*2
*1
*0
Initial Reset
0
0
0
0
0
0
0
0
0
0
0
External Interrupt
0
0
0
0
0
0
0
0
1
0
0
Timer/Event Counter Overflow
0
0
0
0
0
0
0
1
0
0
0
A/D Converter Interrupt
I
2
C BUS Interrupt
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
1
0
0
0
0
Skip
PC+2
Loading PCL
*10
*9
*8
@7
@6
@5
@4
@3
@2
@1
@0
Jump, Call Branch
#10
#9
#8
#7
#6
#5
#4
#3
#2
#1
#0
Return from Subroutine
S10
S9
S8
S7
S6
S5
S4
S3
S2
S1
S0
Program counter
Note: *10~*0: Program counter bits
S10~S0: Stack register bits
#10~#0: Instruction code bits
@7~@0: PCL bits