HT46R46/C46/R47/C47/R48A/C48A/R49
Rev. 1.41
9
December 30, 2008
Program Counter
During program execution, the Program Counter is used
to keep track of the address of the next instruction to be
executed. It is automatically incremented by one each
time an instruction is executed except for instructions,
such as
²
JMP
²
or
²
CALL
²
that demand a jump to a
non-consecutive Program Memory address. For the
Cost-Effective A/D Type series of microcontrollers, note
that the Program Counter width varies with the Program
Memory capacity depending upon which device is se-
lected. However, it must be noted that only the lower 8
bits, known as the Program Counter Low Register, are
directly addressable by user.
When executing instructions requiring jumps to
non-consecutive addresses such as a jump instruction,
a subroutine call, interrupt or reset, etc., the
microcontroller manages program control by loading the
required address into the Program Counter. For condi-
tional skip instructions, once the condition has been
met, the next instruction, which has already been
fetched during the present instruction execution, is dis-
carded and a dummy cycle takes its place while the cor-
rect instruction is obtained.
The lower byte of the Program Counter, known as the
Program Counter Low register or PCL, is available for
program control and is a readable and writable register.
By transferring data directly into this register, a short
program jump can be executed directly, however, as
only this low byte is available for manipulation, the
jumps are limited to the present page of memory, that is
256 locations. When such program jumps are executed
it should also be noted that a dummy cycle will be in-
serted.
The lower byte of the Program Counter is fully accessi-
ble under program control. Manipulating the PCL might
cause program branching, so an extra cycle is needed
to pre-fetch. Further information on the PCL register can
be found in the Special Function Register section.
Mode
Program Counter Bits
b11
b10
b9
b8
b7
b6
b5
b4
b3
b2
b1
b0
Initial Reset
0
0
0
0
0
0
0
0
0
0
0
0
External Interrupt
0
0
0
0
0
0
0
0
0
1
0
0
T i m e r / E v e n t
C o u n t e r
Overflow
0
0
0
0
0
0
0
0
1
0
0
0
A/D Converter Interrupt
0
0
0
0
0
0
0
0
1
1
0
0
Skip
Program C 2
Loading PCL
PC11 PC10
PC9
PC8
@7
@6
@5
@4
@3
@2
@1
@0
Jump, Call Branch
#11
#10
#9
#8
#7
#6
#5
#4
#3
#2
#1
#0
Return from Subroutine
S11
S10
S9
S8
S7
S6
S5
S4
S3
S2
S1
S0
Program Counter
Note:
PC11~PC8: Current Program Counter bits
@7~@0: PCL bits
#11~#0: Instruction code address bits
S11~S0: Stack register bits
For the HT46R49, the Program Counter is 12 bits wide, i.e. from b11~b0.
For the HT46R47 and HT46R48A, the Program Counter is 11 bits wide, i.e. From
b10~b0, therefore the b11 column in the table is not applicable.
For the HT46R46, the Program Counter is 10 bits wide, i.e. from b9~b0, therefore the b11 and
b10 the columns in the table are not applicable.
