HT37B90 datasheet(10/80 Pages) HOLTEK

10 / 80 page

HT37B90/HT37B70/HT37B50/HT37B30

Rev.1.00

June22,2017

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-

rectinstructionisobtained.

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

befoundintheSpecialFunctionRegistersection.

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.

Mode

ProgramCounter

b18~b13

b12 b11 b10

InitialReset

000000

Timer/EventCounter0

Overflow

000000

Timer/EventCounter1

Overflow

000000

TimerCounter2

Overflow(UART)

000000

ERCOCI Interrupt

000000

ADPCM Interrupt

000000

Skip

ProgramCounter+2(WithinCurrentBank)

Loading PCL

P18~P13

P12 P11 P10

Jump,CallBranch

BP1.5~BP1.0 #12 #11 #10

ReturnfromSubroutine

S18~S13

S12 S11 S10

ProgramCounter

Note:

P18~P8:ProgramCounterbits

@7~@0: PCL bits

#12~#0:Instructioncodeaddressbits

BP1.5~BP1.0:ROMbankpointer

S18~S0:Stackregisterbits

FortheHT37B90,theProgramCounteris19bitswide, i.e.fromb18~b0.

FortheHT37B70,theProgramCounteris18bitswide, i.e.fromb17~b0,thereforetheb18columninthe

tableisnotapplicable.

For the HT37B50, the Program Counter is 17 bits wide, i.e. from b16~b0, therefore the b17 and b18 column in

thetableisnotapplicable.

For the HT37B30, the Program Counter is 16 bits wide, i.e. from b15~b0, therefore the b18, b17 and b16 the

columnsinthetablearenotapplicable.

HT37B90 Datasheet(PDF) 10 Page - Holtek Semiconductor Inc

HT37B90 Datasheet(HTML) 10 Page - Holtek Semiconductor Inc

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