ht82m99e Holtek Semiconductor Inc., ht82m99e Datasheet - Page 7

• Manufacturer Part Number: ht82m99e
• Description: Ht82m99e/ht82m99a -- Usb Mouse Encoder 8-bit Mcu
• 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 counter only. The
stack is organized into 4 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.
If the stack is full and a non-masked interrupt takes
place, the interrupt request flag will be recorded but the
acknowledge signal will be inhibited. When the stack
pointer is decremented (by RET or RETI), the interrupt
will be serviced. This feature prevents stack overflow al-
lowing the programmer to use the structure more easily.
In a similar case, if the stack is full and a CALL is sub-
sequently executed, stack overflow occurs and the first
entry will be lost (only the most recent 4 return ad-
dresses are stored).
Data Memory - RAM for Bank 0
The data memory is designed with 96 8 bits. The data
memory is divided into two functional groups: special
function registers and general purpose data memory
(96 8). Most are read/write, but some are read only.
The unused space before 20H is reserved for future ex-
panded usage and reading these locations will get
from 20H to 7FH, is used for data and control informa-
tion under instruction commands.
All of the data memory areas can handle arithmetic,
logic, increment, decrement and rotate operations di-
rectly. Except for some dedicated bits, each bit in the
data memory can be set and reset by SET [m].i and
memory pointer registers (MP0 or MP1).
Rev. 2.20
00H . The general purpose data memory, addressed
CLR [m].i . They are also indirectly accessible through
7
Bank 0 RAM Mapping
HT82M99E/HT82M99A
April 16, 2008