HT47C20 datasheet(9/46 Pages) HOLTEK

9 / 46 page

HT47C20

Rev. 1.60

July 26, 2002

Program memory

- ROM

The program memory is used to store the program in-

structions which are to be executed. It also contains

data, table, and interrupt entries, and is organized into

2048

´16 bits, addressed by the program counter and ta-

ble pointer.

Certain locations in the program memory are reserved

for special usage

· Location 000H

This area is reserved for the initialization program. Af-

ter chip reset, the program always begins execution at

location 000H.

· Location 004H

This area is reserved for the external interrupt service

program. If the INT input pin is activated, and the inter-

rupt is enabled and the stack is not full, the program

begins execution at location 004H.

· Location 008H

This area is reserved for the time base interrupt service

program. If time base interrupt results from a time base

overflow, and if the interrupt is enabled and the stack is

not full, the program begins execution at location 008H.

· Location 00CH

This area is reserved for the real time clock interrupt

service program. If a real time clock interrupt results

from a real time clock overflow, and if the interrupt is

enabled and the stack is not full, the program begins

execution at location 00CH.

· Location 010H

This area is reserved for the timer/event counter inter-

rupt service program. If a timer interrupt results from a

Timer/Event Counter A or B overflow, and if the inter-

rupt is enabled and the stack is not full, the program

begins execution at location 010H.

· Table location

Any location in the ROM space can be used as look up

tables. The instructions TABRDC [m] (the current

page, 1 page=256 words) and TABRDL [m] (the last

page) transfer the contents of the lower-order byte to

the specified data memory, and the higher-order byte

to TBLH (08H). Only the destination of the lower-order

byte in the table is well-defined, the higher-order byte

of the table word are transferred to the TBLH. The ta-

ble higher-order byte register (TBLH) is read only. The

table pointer (TBLP) is a read/write register (07H),

which indicates the table location. Before accessing

the table, the location must be placed in TBLP. The

TBLH is read only and cannot be restored. If the main

routine and the ISR (Interrupt Service Routine) both

employ the table read instruction, the contents of the

TBLH in the main routine are likely to be changed by

the table read instruction used in the ISR. Errors can

occur. In other words, using the table read instruction

in the main routine and the ISR simultaneously should

be avoided. However, if the table read instruction has

to be applied in both the main routine and the ISR, the

interrupt is supposed to be disabled prior to the table

read instruction. It will not be enabled until the TBLH

has been backed up. All table related instructions

need two cycles to complete the operation. These ar-

eas may function as normal program memory depend-

ing upon the requirements.

0 0 0 H

0 0 4 H

0 0 8 H

D e v i c e i n i t i a l i z a t i o n p r o g r a m

E x t e r n a l i n t e r r u p t s u b r o u t i n e

P r o g r a m

R O M

1 6 b i t s

L o o k - u p t a b l e ( 2 5 6 w o r d s )

7 . . H

N o t e : n r a n g e s f r o m 0 t o 7

0 0 C H

T i m e b a s e i n t e r r u p t s u b r o u t i n e

R T C i n t e r r u p t s u b r o u t i n e

L o o k - u p t a b l e ( 2 5 6 w o r d s )

n 0 0 H

n . . H

T i m e r / e v e n t c o u n t e r i n t e r r u p t s u b r o u t i n e

0 1 0 H

Program memory

Instruction(s)

Table Location

*10

TABRDC [m]

P10

TABRDL [m]

Table location

Note: *10~*0: Table location bits

@7~@0: Table pointer bits

P10

~P8: Current program counter bits

HT47C20 Datasheet(PDF) 9 Page - Holtek Semiconductor Inc

HT47C20 Datasheet(HTML) 9 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Datasheet Download

Link URL