HT9480 datasheet(8/57 Pages) HOLTEK

8 / 57 page

The PC value is incremented by one after a

program memory word is accessed in order to

fetch an instruction code. The PC then points to

a memory word with the next instruction code.

The PC loads the address corresponding to each

instruction and then manipulates program

transfer while executing a jump instruction,

conditional skip execution, loading a PCL, a

internal interrupt, an external interrupt, or re-

turning from a subroutine.

The conditional skip is activated by instruc-

tions. Once the condition is satisfied, the next

instruction, fetched during the current instruc-

tion execution, is discarded, and a dummy cycle

is replaced to get a proper instruction. Other-

wise it proceeds with the following instruction.

The low byte of the PC (PCL) is a readable and

writable register (06H). Moving data into the

PCL performs a short jump. The destination is

within 256 locations.

If a control transfer takes place, an additional

dummy cycle is required.

Program memory – ROM

The program memory (ROM) is used to store

the program instructions that are to be exe-

cuted. It consists of data, table(s), and interrupt

entries, and is organized into 8192

×16 bits,

which are addressed by the PC and table pointer.

Certain locations in the ROM are reserved for

specific usage:

• Location 0000H

Location 0000H is reserved for program in-

itialization. The program always begins exe-

cution at this location each time the chip is

reset.

• Location 0004H

Location 0004H is reserved for the data ready

interrupt and battery fail interrupt service

programs. If an interrupt results from a pager

decoder interrupt request or from a battery

fail interrupt request, and the interrupt is

enabled, and the stack is not full, the program

begins execution at location 0004H. The oc-

currence of a data ready interrupt or a battery

fail interrupt is detected by checking the bat-

tery fail interrupt bit (1EH-bit 4, BF flag) and

the data ready interrupt bit (1EH-bit 7, DR

flag). The interrupt should be carefully proc-

essed if both interrupt bits are active.

• Location 0008H

Location 0008H is reserved for the program-

mable timer interrupt service program. If an

interrupt results from a programmable timer

interrupt request (its source is from 256Hz

divided by N, where the value of N ranges

from 1 to 256.), and the interrupt is enabled,

and the stack is not full, the program begins

execution at location 0008H.

• Location 000CH

Location 000CH is reserved for the timer/event

counter interrupt service program. If a timer

interrupt results from a timer/event counter

overflow, and the interrupt is enabled, and the

stack is not full, the program begins execution

at location 000CH.

• Look-up tables XX00H~XXFFH

The ROM is composed of 32 groups (each

group contains 256 continuous words) which

can be used as look–up tables. The instruc-

tions “TABRDC [m]” (the current table) and

“TABRDL [m]” (the last table) transfer the

contents of the low-order byte to the specified

data memory, and the contents of the high-or-

der byte to TBLH (Table High-order Byte Reg-

Program memory

HT9480

23th Feb ’98

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