ht82m9aae Holtek Semiconductor Inc., ht82m9aae Datasheet - Page 8

• Manufacturer Part Number: ht82m9aae
• Description: Usb Mouse Encoder 8-bit Mcu With Eeprom
• 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 ²CALL² 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 224´8 bits. The data
memory is divided into two functional groups: special
function registers and general purpose data memory
(224´8). Most are read/write, but some are read only.
The unused spaces before the 20H is reserved for fu-
ture expanded usage and reading these locations will
get ²00H². The general purpose data memory, ad-
dressed from 20H to FFH, is used for data and control
information 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 ²SET [m].i² and
²CLR [m].i². They are also indirectly accessible through
memory pointer registers (MP0 or MP1).
Data Memory - RAM for Bank 1
The special function registers used in the USB interface
are located in RAM Bank1. In order to access Bank1
register, only the Indirect addressing pointer MP1 can
be used and the Bank register BP should be set to 1.
The RAM bank 1 mapping is as shown.
Address 00~1FH in RAM Bank0 and Bank1 are located
in the same Registers
Rev. 1.20
8
Indirect Addressing Register
Locations 00H and 02H are indirect addressing regis-
ters that are not physically implemented. Any read/write
operation on [00H] ([02H]) will access the data memory
pointed to by MP0 (MP1). Reading location 00H (02H)
indirectly will return the result 00H. Writing indirectly re-
sults in no operation.
The indirect addressing pointer (MP0) always points to
Bank0 RAM addresses no matter the value of Bank
Register (BP).
The indirect addressing pointer (MP1) can access
Bank0 or Bank1 RAM data according to the value of BP
which is set to ²0² or ²1² respectively.
The memory pointer registers (MP0 and MP1) are 8-bit
registers.
HT82M9AEE/HT82M9AAE
Bank 0 RAM Mapping
August 13, 2007