HT48R50A-1/HT48C50-1
·
Table location
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Any location in the ROM space can be used as
look-up tables. The instructions ²TABRDC [m]² (the
current page, one page=256 words) and ²TABRDL
[m]² (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 desti-
nation of the lower-order byte in the table is
well-defined, the other bits of the table word are trans-
ferred to the lower portion of TBLH, and the remaining
1-bit words are read as ²0². The Table 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 lo-
cation must be placed in the 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 rou-
tine 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 in-
struction. It will not be enabled until the TBLH has
been backed up. All table related instructions require
two cycles to complete the operation. These areas
may function as normal program memory depending
upon the requirements.
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Program Memory
Certain locations in the program memory are reserved
for special usage:
·
Location 000H
This area is reserved for program initialization. After
chip reset, the program always begins execution at lo-
cation 000H.
·
Location 004H
This area is reserved for the external interrupt service
program. If the INT input pin is activated, the interrupt
is enabled and the stack is not full, the program begins
execution at location 004H.
Stack Register - STACK
·
·
Location 008H
This is a special part of the memory which is used to
save the contents of the Program Counter only. The
stack is organized into 6 levels and is neither part of the
data nor part of the program space, and is neither read-
able nor writeable. The activated level is indexed by the
stack pointer (SP) and is neither readable nor writeable.
At a subroutine call or interrupt acknowledge signal, 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.
This area is reserved for the Timer/Event Counter 0 in-
terrupt service program. If a timer interrupt results from a
Timer/Event Counter 0 overflow, and if the interrupt is
enabled and the stack is not full, the program begins ex-
ecution at location 008H.
Location 00CH
This location is reserved for the Timer/Event Counter
1 interrupt service program. If a timer interrupt results
from a Timer/Event Counter 1 overflow, and the inter-
rupt is enabled and the stack is not full, the program
begins execution at location 00CH.
Table Location
Instruction
*11
P11
1
*10
P10
1
*9
P9
1
*8
P8
1
*7
*6
*5
*4
*3
*2
*1
*0
TABRDC [m]
TABRDL [m]
@7
@7
@6
@6
@5
@5
@4
@4
@3
@3
@2
@2
@1
@1
@0
@0
Table Location
P11~P8: Current program counter bits
Note: *11~*0: Table location bits
@7~@0: Table pointer bits
Rev. 2.00
7
March 8, 2006
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
