sh66k31c SinoWealth Micro-Electronics Corp. Ltd, sh66k31c Datasheet - Page 4

• Manufacturer Part Number: sh66k31c
• Description: Mask 4-bit Micro-controller
• Manufacturer: SinoWealth Micro-Electronics Corp. Ltd

Functional Description
1. CPU
The CPU contains the following functional blocks: Program
Counter (PC), Arithmetic Logic Unit (ALU), Carry Flag (CY),
Accumulator, Table Branch Register, Data Pointer (INX,
DPH, DPM, and DPL) and Stacks.
1.1. PC
The PC is used for ROM addressing consisting of 12-bit:
Page Register (PC11), and Ripple Carry Counter (PC10,
PC9, PC8, PC7, PC6, PC5, PC4, PC3, PC2, PC1, PC0).
The program counter is loaded with data corresponding to
each instruction. The unconditional jump instruction (JMP)
can be set at 1-bit page register for higher than 2K.
The program counter cans only 4K program ROM address.
(Refer to the ROM description).
1.2. ALU and CY
The ALU performs arithmetic and logic operations. The ALU
provides the following functions:
Binary addition/subtraction (ADC, SBC, ADD, SUB, ADI, SBI)
Decimal adjustments for addition/subtraction (DAA, DAS)
Logic operations (AND, EOR, OR, ANDIM, EORIM, ORIM)
Decisions (BA0, BA1, BA2, BA3, BAZ, BNZ, BC, BNC)
Logic Shift (SHR)
The Carry Flag (CY) holds the ALU overflow that the
arithmetic operation generates. During an interrupt service
or CALL instruction, the carry flag is pushed into the stack
and recovered from the stack by the RTNI instruction. It is
unaffected by the RTNW instruction.
1.3. Accumulator (AC)
The accumulator is a 4-bit register holding the results of the
arithmetic logic unit. In conjunction with the ALU, data is
transferred between the accumulator and system register, or
data memory can be performed.
2. RAM
Built-in RAM contains general-purpose data memory and system register. Because of its static nature, the RAM can keep data
after the CPU enters STOP or HALT.
2.1. RAM Addressing
Data memory and system register can be accessed in one instruction by direct addressing. The following is the memory allocation
map:
System Register and I/O: $000 - $01F
Data memory: $020 - $04F
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1.4. Table Branch Register (TBR)
Table Data can be stored in program memory and can be
referenced by using Table Branch (TJMP) and Return
Constant (RTNW) instructions. The TBR and AC are placed
by an offset address in program ROM. TJMP instruction
branch into address ((PC11 - PC8) X (28) + (TBR, AC)). The
address is determined by RTNW to return look-up value into
(TBR, AC). ROM code bit7 - bit4 is placed into TBR and
bit3-bit0 into AC.
1.5. Data Pointer
The Data Pointer can indirectly address data memory.
Pointer address is located in register DPH (3-bit), DPM
(3-bit) and DPL (4-bit). The addressing range can have
3FFH locations. Pseudo index address (INX) is used to read
or write Data memory, then RAM address bit9 - bit0 comes
from DPH, DPM and DPL.
1.6. Stack
The stack is a group of registers used to save the contents of
CY & PC (11-0) sequentially with each subroutine call or
interrupt. The MSB is saved for CY and it is organized into 13
bits X 4 levels. The stack is operated on a first-in, last-out
basis and returned sequentially to the PC with the return
instructions (RTNI/RTNW).
Note:
The stack nesting includes both subroutine calls and
interrupt requests. The maximum allowed for subroutine
calls and interrupts are 4 levels. If the number of calls and
interrupt requests exceeds 4, then the bottom of stack will be
shifted out, that program execution may enter an abnormal
state.
SH66K31C