HT49R30A-1/HT49C30-1/HT49C30L
Functional Description
Execution flow
The system clock is derived from either a crystal or an
RC oscillator or a 32768Hz crystal oscillator. It is inter-
nally divided into four non-overlapping clocks. One in-
struction cycle consists of four system clock cycles.
Instruction fetching and execution are pipelined in such
a way that a fetch takes one instruction cycle while de-
coding and execution takes the next instruction cycle.
The pipelining scheme causes each instruction to effec-
tively execute in a cycle. If an instruction changes the
value of the program counter, two cycles are required to
complete the instruction.
Program counter
-
PC
The program counter (PC) is of 11 bits wide and controls
the sequence in which the instructions stored in the pro-
gram ROM are executed. The contents of the PC can
specify a maximum of 2048 addresses.
After accessing a program memory word to fetch an in-
struction code, the value of the PC is incremented by
one. The PC then points to the memory word containing
the next instruction code.
When executing a jump instruction, conditional skip ex-
ecution, loading a PCL register, a subroutine call, an ini-
tial reset, an internal interrupt, an external interrupt, or
returning from a 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 a proper instruction; oth-
erwise proceed with the next instruction.
The lower byte of the PC (PCL) is a readable and
writeable register (06H). Moving data into the PCL per-
forms a short jump. The destination is within 256 loca-
tions.
T 2
T 3
T 4
T 1
T 2
T 3
T 4
S y s te m
C lo c k
T 1
T 2
T 3
T 4
T 1
O S C 2 ( R C o n ly )
P C
P C
P C + 1
P C + 2
. e tc h IN S T (P C )
E x e c u te IN S T (P C -1 )
. e tc h IN S T (P C + 1 )
E x e c u te IN S T (P C )
. e tc h IN S T (P C + 2 )
E x e c u te IN S T (P C + 1 )
Execution flow
Program Counter
*10
0
0
0
0
0
0
*9
0
0
0
0
0
0
*8
0
0
0
0
0
0
*7
0
0
0
0
0
0
*6
0
0
0
0
0
0
*5
0
0
0
0
0
0
PC+2
*10
#10
S10
*9
#9
S9
*8
#8
S8
@7
#7
S7
@6
#6
S6
@5
#5
S5
@4
#4
S4
@3
#3
S3
@2
#2
S2
@1
#1
S1
@0
#0
S0
*4
0
0
0
0
1
1
*3
0
0
1
1
0
0
*2
0
1
0
1
0
1
*1
0
0
0
0
0
0
*0
0
0
0
0
0
0
Mode
Initial Reset
External Interrupt 0
External Interrupt 1
Timer/Event Counter Overflow
Time Base Interrupt
RTC Interrupt
Skip
Loading PCL
Jump, Call Branch
Return From Subroutine
Program counter
Note: *10~*0: Program counter bits
#10~#0: Instruction code bits
S10~S0: Stack register bits
@7~@0: PCL bits
Rev. 1.10
8
September 25, 2002
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
