Holtek HT827A0 Manual page 9

Program memory - ROM
The program memory stores the to-be-executed
program instructions. It also includes data, ta-
ble and interrupt entries, addressed by the pro-
gram counter along with the table pointer.
The program memory size for HT827A0 is
8K´16.
Certain locations in the program memory are
reserved for special usage:
· Location 000H
This area is reserved for program initializa-
tion. The program always begins execution at
location 000H each time the system is reset.
· Location 004H
This area is reserved for an external interrupt
service program. The program begins execu-
tion at location 004H if the INT input pin is
activated, the interrupt is enabled and the
stack is not full.
·
Location 008H
This area is reserved for a voice sampling rate
counter interrupt service program. The pro-
gram begins execution at location 008H if a
timer interrupt results from a sampling rate
Mode
Initial reset
External interrupt
Sampling rate counter
overflow
Timer/event counter
overflow
Skip
Loading PCL
Jump, call branch
Return from subroutine
Note: *12~*0: Bits of program counter
#12~#0: Bits of instruction code
0 0 0 H
0 0 4 H
0 0 8 H
0 0 C H
1 F F F H
counter overflow, the interrupt is enabled and
the stack is not full.
· Location 00CH
This area is reserved for a timer/event coun-
ter interrupt service program. The program
begins execution at location 00CH if an inter-
rupt results from a timer/event counter over-
flow, the interrupt is enabled and the stack is
not full.
Program Counter
*12 *11 *10 *9 *8
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
*12 *11 *10 *9 *8 @7
#12 #11 #10 #9 #8
S12 S11 S10 S9 S8 S7
Program counter
9
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
S a m p l i n g r a t e 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
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
L o o k - u p t a b l e ( 2 5 6 w o r d s )
L o o k - u p t a b l e ( 2 5 6 w o r d s )
Program memory
*7 *6 *5 *4 *3 *2
0 0 0 0 0
0 0 0 0 0
0 0 0 0 1
0 0 0 0 1
PC+2
@6 @5 @4 @3 @2
#7 #6 #5 #4 #3 #2
S6 S5 S4 S3 S2
S12~S0: Bits of stack register
@7~@0: Bits of PCL
HT827A0
P r o g r a m
R O M
*1 *0
0 0 0
1 0 0
0 0 0
1 0 0
@1 @0
#1 #0
S1 S0
March 15, 2000