HT37B90/HT37B70/HT37B50/HT37B30
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 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.
Stack
This is a special part of the memory which is used to
save the contents of the Program Counter only. The
stack can have 12 levels depending upon which option
is selected and is neither part of the data nor part of the
program space, and is neither readable nor writable.
The activated level is indexed by the Stack Pointer, SP,
and is neither readable nor writable. At a subroutine call
or interrupt acknowledge signal, the contents of the Pro-
gram Counter are pushed onto the stack. At the end of a
subroutine or an interrupt routine, signaled by a return
instruction, RET or RETI, the Program Counter is re-
stored to its previous value from the stack. After a de-
vice reset, the Stack Pointer will point to the top of the
stack.
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.
Program Counter
Mode
b18~b13
b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
Initial Reset
000000
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
Timer/Event Counter 0
Overflow
000000
000000
000000
Timer/Event Counter 1
Overflow
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
0
0
0
0
Timer Counter 2
Overflow (UART)
ERCOCI Interrupt
ADPCM Interrupt
Skip
000000
000000
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
1
1
0
0
0
0
0
Program Counter + 2 (Within Current Bank)
P12 P11 P10 P9 P8 @7 @6 @5 @4 @3 @2 @1 @0
Loading PCL
Jump, Call Branch
P18~P13
BP1.5~BP1.0 #12 #11 #10 #9 #8 #7 #6 #5 #4 #3 #2 #1 #0
Return from Subroutine S18~S13
S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 S1 S0
Program Counter
Note: P18~P8: Program Counter bits
@7~@0: PCL bits
#12~#0: Instruction code address bits
BP1.5~BP1.0: ROM bank pointer
S18~S0: Stack register bits
For the HT37B90, the Program Counter is 19 bits wide, i.e. from b18~b0.
For the HT37B70, the Program Counter is 18 bits wide, i.e. from b17~b0, therefore the b18 column in the
table is not applicable.
For the HT37B50, the Program Counter is 17 bits wide, i.e. from b16~b0, therefore the b17 and b18 column in
the table is not applicable.
For the HT37B30, the Program Counter is 16 bits wide, i.e. from b15~b0, therefore the b18, b17 and b16 the
columns in the table are not applicable.
Rev. 1.00
10
June 22, 2017
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
