sh6620a SinoWealth Micro-Electronics Corp. Ltd, sh6620a Datasheet - Page 3

• Manufacturer Part Number: sh6620a
• Description: Mask 4-bit Microcontroller
• Manufacturer: SinoWealth Micro-Electronics Corp. Ltd

Functional Description
1. CPU
The CPU contains the following function blocks: Program
Counter,
Accumulator, Table Branch Register, Data Pointer (INX,
DPH, DPM, and DPL), and Stack.
1.1. PC (Program Counter)
The Program Counter is used to address the 1K program
ROM. It consists of 12-bits: Page Register (PC11), and
Ripple Carry Counter (PC10, PC9, PC8, PC7, PC6, PC5,
PC4, PC3, PC2, PC1, PC0).
The program counter normally increases by one (+1) with
every execution of an instruction except in the following
cases:
(1) When executing a jump instruction (such as JMP, BA0,
(2) When executing a subroutine call instruction (CALL),
(3) When an interrupt occurs,
(4) When the chip is at the INITIAL RESET mode.
The program counter is loaded with data corresponding to
each instruction.
1.2. ALU and CY
ALU performs arithmetic and logic operations. The ALU
provides the following functions:
Binary addition/subtraction (ADC, SBC, ADD, SUB, ADI,
SBI)
Decimal adjust for addition/subtraction (DAA, DAS) Logic
2
The SH6620A can be addressed up to 1024 X 16 bit of program area from $000 to $3FF.
Service routine as the starting vector address.
Vector Address Area ($000 to $004)
The program is sequentially executed. There is an area address $000 through $004 that is reserved for a special interrupt
service routine such as the starting vector address.
.
Address
ROM
$000H
$001H
$002H
$003H
$004H
BC),
Arithmetic
JMP instruction
JMP instruction
JMP instruction
Instruction
Logic
NOP
NOP
Unit
(ALU),
Jump to RESET service routine
Reserved
Jump to TIMER0 service routine
Reserved
Jump to PBC service routine
Carry
Flag,
Remarks
3
operations (AND, EOR, OR, ANDIM, EORIM, ORIM)
Decision (BA0, BA1, BA2, BA3, BAZ, BC)
Logic Shift (SHR)
The Carry Flag (CY) holds the ALU overflow which the
arithmetic operation generates. During an interrupt servicing
or call instruction, the carry flag is pushed into the stack and
restored back from the stack by the RTNI instruction. It is
unaffected by the RTNW instruction.
1.3
Accumulator is a 4-bit register holding the results of the
arithmetic logic unit. In conjunction with ALU, data transfer
between the accumulator and system register, or data
memory can be performed.
1.4
A group of registers are used to save the contents of CY &
PC (11-0) sequentially with each subroutine call or interrupt.
It is organized 13 bits X 4 levels. The MSB is saved for CY. 4
levels are the maximum allowed for subroutine calls and
interrupts.
The contents of Stack are returned sequentially to the PC
with the return instructions (RTNI/RTNW). Stack is operated
on a first-in, last-out basis. This 4-level nesting includes both
subroutine call and interrupt requests. Note that program
execution may enter an abnormal state if the number of calls
and interrupt requests exceed 4, and the bottom of stack will
be shifted out.
.
.
Accumulator
Stack
SH6620A