HT82K68 Holtek Semiconductor Inc, HT82K68 Datasheet - Page 9

• Manufacturer Part Number: HT82K68
• Description: Multimedia Keyboard Encoder OTP
• Manufacturer: Holtek Semiconductor Inc

Stack register - STACK
This is a special part of the memory which is
used to save the contents of the program coun-
ter (PC) only. The stack is organized into six lev-
els and is neither part of the data nor part of the
program space, and is neither readable nor
writeable. The activated level is indexed by the
stack pointer (SP) and is neither readable nor
writeable. At a subroutine call or interrupt ac-
knowledgement, the contents of the program
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 pro-
gram counter is restored to its previous value
from the stack. After a chip reset, the SP will
point to the top of the stack.
If the stack is full and a non-masked interrupt
takes place, the interrupt request flag will be re-
corded but the acknowledgement will be inhib-
ited. When the stack pointer is decremented (by
RET or RETI), the interrupt will be serviced. This
feature prevents stack overflow allowing the pro-
grammer to use the structure more easily. In a
similar case, if the stack is full and a ²CALL² is
subsequently executed, stack overflow occurs and
the first entry will be lost (only the most recent
four return addresses are stored).
Data memory - RAM
The data memory is designed with 184 ´ 8 bits.
It is divided into two functional groups: special
function registers and general purpose data
memory (160´8). Most of them are read/write,
but some are read only.
The special function registers include the Indi-
rect Addressing register 0 (00H), the Memory
Pointer register 0 (MP0;01H), the Indirect Ad-
dressing register 1 (02H), the Memory Pointer
register 1 (MP1;03H), the Accumulator
Note: *11~*0: Table location bits
TABRDC [m]
TABRDL [m]
Instruction(s)
@7~@0: Table location bits
P11
*11
1
P10
*10
0
P9
*9
1
Preliminary
P8
*8
1
@7
@7
*7
9
Table Location
(ACC;05H), the Program Counter Lower-byte
register (PCL;06H), the Table Pointer
(TBLP;07H), the Table Higher-order byte regis-
ter (TBLH;08H), the Watchdog Timer option Set-
ting register (WDTS;09H), the Status register
P11~P8: Current program counter bits
@6
@6
*6
@5
@5
*5
RAM mapping
@4
@4
*4
@3
@3
*3
@2
@2
*2
HT82K68E
August 8, 2000
@1
@1
*1
²
²
@0
@0
*0