HT47C20 Holtek Semiconductor Inc, HT47C20 Datasheet - Page 11

• Manufacturer Part Number: HT47C20
• Description: 8-Bit Microcontroller
• Manufacturer: Holtek Semiconductor Inc

Note: *10~*0: Table location bits
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 four
levels 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-
knowledgment, 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
TABRDC [m]
TABRDL [m]
Instruction(s)
must be placed in TBLP. The TBLH is read
only and cannot be restored. If the main rou-
tine 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 instruc-
tion used in the ISR. Errors can occur. In
other words, using the table read instruction
in the main routine and the ISR simulta-
neously should be avoided. However, if the ta-
ble 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 areas may function as nor-
mal program memory depending upon the re-
quirements.
P10~P8: Current program counter bits
P10
*10
1
P9
*9
1
P8
*8
1
Table location
@7
@7
*7
11
@6
@6
Table Location
*6
recorded but the acknowledgment 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 programmer to use the structure more eas-
ily. In a similar case, if the stack is full and a
²CALL² is subsequently executed, stack over-
flow 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 83 ´ 8 bits.
The data memory and is divided into two func-
tional groups: special function registers and
general purpose data memory (64´ 8). Most 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 bank pointer
(BP;04H), the accumulator (ACC;05H), the pro-
gram counter lower-order byte register
(PCL;06H), the table pointer (TBLP;07H), the
table higher-order byte register (TBLH;08H),
the real time clock control register (RTCC;09H),
the status register (STATUS;0AH), the inter-
rupt control register 0 (INTC0;0BH), the I/O reg-
isters (PA;12H, PB;14H), the interrupt control
register 1 (INTC1;1EH), the timer/event counter
A higher order byte register (TMRAH; 20H), the
timer/event counter A lower order byte register
(TMRAL; 21H), the timer/event counter control
register (TMRC; 22H), the timer/event counter B
higher order byte register (TMRBH; 23H), the
timer/event counter B lower order byte register
(TMRBL; 24H), and the RC oscillator type A/D
@7~@0: Table pointer bits
@5
@5
*5
@4
@4
*4
@3
@3
*3
@2
@2
*2
January 18, 2000
HT47C20
@1
@1
*1
@0
@0
*0