HMS87C1808B Datasheet, PDF (27/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
8. MEMORY ORGANIZATION
The HMS87C1X04B/08B/16B has separate address spaces for
Program memory and Data Memory. The Program memory can
only be read, not written to. It can be up to 4K /8K /16K bytes of
8.1 Registers
This device has six registers that are the Program Counter (PC),
a Accumulator (A), two index registers (X, Y), the Stack Pointer
(SP), and the Program Status Word (PSW). The Program Counter
consists of 16-bit register.
PCH
A
X
Y
SP
PCL
PSW
ACCUMULATOR
X REGISTER
Y REGISTER
STACK POINTER
PROGRAM COUNTER
PROGRAM STATUS
WORD
Figure 8-1 Configuration of Registers
Accumulator: The Accumulator is the 8-bit general purpose reg-
ister, used for data operation such as transfer, temporary saving,
and conditional judgement, etc.
The Accumulator can be used as a 16-bit register with Y Register
as shown below.
Y
Y
A
A
Two 8-bit Registers can be used as a “YA” 16-bit Register
Figure 8-2 Configuration of YA 16-bit Register
X, Y Registers: In the addressing mode which uses these index
registers, the register contents are added to the specified address,
which becomes the actual address. These modes are extremely ef-
fective for referencing subroutine tables and memory tables. The
index registers also have increment, decrement, comparison and
data transfer functions, and they can be used as simple accumula-
tors.
Stack Pointer: The Stack Pointer is an 8-bit register used for oc-
currence interrupts and calling out subroutines. Stack Pointer
identifies the location in the stack to be accessed (save or restore).
Program memory. The Data memory can be read and written to
up to 448 bytes including the stack area.
Generally, SP is automatically updated when a subroutine call is
executed or an interrupt is accepted. However, if it is used in ex-
cess of the stack area permitted by the data memory allocating
configuration, the user-processed data may be lost.
The stack can be located at any position within 00_H to BF_H of the
internal data memory. The SP is not initialized by hardware, re-
quiring to write the initial value (the location with which the use
of the stack starts) by using the initialization routine. Normally,
the initial value of “BF_H” is used.
Stack Address (00_H ~ BF_H)
15
87
0
00
SP
Hardware fixed
Note: The Stack Pointer must be initialized by software be-
cause its value is undefined after RESET.
Example: To initialize the SP
LDX
#0BFH
TXSP
; SP ← BF_H
Program Counter: The Program Counter is a 16-bit wide which
consists of two 8-bit registers, PCH and PCL. This counter indi-
cates the address of the next instruction to be executed. In reset
state, the program counter has reset routine address (PC_H:0FF_H,
PC_L:0FE_H).
Program Status Word: The Program Status Word (PSW) con-
tains several bits that reflect the current state of the CPU. The
PSW is described in Figure 8-3 . It contains the Negative flag, the
Overflow flag, Direct page select flag, the Break flag, the Half
Carry (for BCD operation), the Interrupt enable flag, the Zero
flag, and the Carry flag.
[Carry flag C]
This flag stores any carry or borrow from the ALU of CPU after
an arithmetic operation and is also changed by the Shift Instruc-
tion or Rotate Instruction.
[Zero flag Z]
This flag is set when the result of an arithmetic operation or data
transfer is “0” and is cleared by any other result.
SEP. 2004 Ver 1.03
23