HT49R50 Holtek Semiconductor Inc, HT49R50 Datasheet - Page 11

• Manufacturer Part Number: HT49R50
• Description: 8-Bit Microcontroller
• Manufacturer: Holtek Semiconductor Inc

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Notes: *11~*0: Table location bits
Instruction(s)
TABRDC [m]
TABRDL [m]
Location 014H
Location 014H is reserved for the Time Base
interrupt service program. If a Time Base in-
terrupt occurs, and the interrupt is enabled,
and the stack is not full, the program begins
execution at location 014H.
Location 018H
Location 018H is reserved for the real time
clock interrupt service program. If a real time
clock interrupt occurs, and the interrupt is
enabled, and the stack is not full, the program
begins execution at location 018H.
Table location
Any location in the ROM can be used as a
look-up table. The instructions ²TABRDC
[m]² (the current page, 1 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 contents of
the higher-order byte to TBLH (Table
Higher-order byte register) (08H). Only the
destination of the lower-order byte in the ta-
ble is well-defined; the other bits of the table
word are all transferred to the lower portion
of TBLH, and the remaining 1 bit is read as
²0². The TBLH is read only, and the table
pointer (TBLP) is a read/write register (07H),
indicating the table location. Before accessing
the table, the location should be placed in
TBLP. All the table related instructions re-
quire 2 cycles to complete the operation.
These areas may function as a normal ROM
depending upon the user¢s requirements.
@7~@0: Table pointer bits
P11
*11
1
P10
*10
1
P9
*9
1
P8
*8
1
Table location
@7
@7
*7
11
Table Location
Stack register - STACK
The stack register is a special part of the mem-
ory used to save the contents of the PC. The
stack is organized into 6 levels and is neither
part of the data nor part of the program, and is
neither readable nor writeable. Its activated
level is indexed by a stack pointer (SP) and is
neither readable nor writeable. At a commence-
ment of a subroutine call or an interrupt ac-
knowledgment, the contents of the PC is
pushed onto the stack. At the end of the subrou-
tine or interrupt routine, signaled by a return
instruction (RET or RETI), the contents of the
PC is restored to its previous value from the
stack. After 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 is re-
corded but the acknowledgment is still inhib-
ited. Once the SP is decremented (by RET or
RETI), the interrupt is serviced. This feature
prevents stack overflow, allowing the program-
mer to use the structure easily. Likewise, if the
stack is full, and a ²CALL² is subsequently exe-
cuted, a stack overflow occurs and the first en-
try is lost (only the most recent six return
addresses are stored).
Data memory - RAM
The data memory (RAM) is designed with
192´8 bits, and is divided into two functional
groups, namely special function registers and
general purpose data memory, most of which
are readable/writeable, although some are read
only.
@6
@6
*6
P11~P8: Current program Counter bits
@5
@5
*5
@4
@4
*4
@3
@3
*3
@2
@2
*2
August 18, 1999
HT49C50
@1
@1
*1
@0
@0
*0