HTG12N0 datasheet(9/30 Pages) HOLTEK

9 / 30 page

• Location 4

Contains the timer interrupt resulting from a

TIMER overflow. If the interrupts are enabled,

it causes the program to jump to this subrou-

tine.

• Location 8

Activating the RTC of the processor with the

interrupts enabled causes the program to

jump to this location.

• Locations n00H to nFFH

Each page in the program memory consists of

256 bytes. This area from n00H to nFFH and

F00H to FFFH can be used as a look-up table.

Instructions such as READ R4A, READ

MR0A, READF R4A, READF MR0A can read

the table and transfer the contents of the

table to ACC and R4 or to ACC and a data

memory address specified by the register pair

R1,R0. However as R1,R0 can only store 8

bits, these instructions cannot fully specify

the full 12-bit program memory address. For

this reason a jump instruction should be used

first to place the program counter in the right

page. The above instructions can then be used

to read the look up table data.

Note that the page number n must be greater

than zero as some locations in page 0 are re-

served for specific usage as mentioned. This

area may function as normal program memory

as required.

The program memory mapping is shown in the

diagram.

In the execution of an instruction the program

counter is added before the execution phase, so

careful manipulation of READ MR0A and

READ R4A is required in the page margin.

Stack register

The stack register is a group of registers used to

save the contents of the program counter (PC)

and is arranged in 13 bits

× 1 level. One bit is

used to store the carry flag. An interrupt will

force the contents of the PC and the carry flag

onto the stack register. A subroutine call will

also cause the PC contents to be pushed onto

the stack; however the carry flag will not be

stored. At the end of a subroutine or an inter-

rupt routine which is signaled by a return in-

struction, RET or RETI restore the program

counter to its previous value from the stack

store the carry flag from the stack register, but

“RET” will not.

Working registers – R0, R1, R2, R3, R4

There are five working registers (R0, R1, R2, R3, R4)

usually used to store the frequently accessed inter-

mediate results. Using the instructions INC Rn and

DEC Rn the working registers can increment (+1) or

decrement (–1). The JNZ Rn (n=0,1,4) instruction

makes efficient use of the working registers as a

program loop counter. Also the register pairs R0,R1

and R2,R3 are used as a data memory pointer when

the memory transfer instruction is executed.

Program memory PB0=1, PB1=1

Program memory PB0=0, PB1=1

HTG12N0

18th Mar ’99

HTG12N0 Scheda tecnica(PDF) 9 Page - Holtek Semiconductor Inc

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