HT48C10 datasheet(13/59 Pages) HOLTEK

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Functional Description

The four microcontrollers of the HT48C10/

HT48C30/HT48C50/HT48C70 are constructed

using basically the same principles. Their dif-

ferences lie in variations in sizes such as ROM

and RAM as well as bit number, counter num-

ber, I/O line number, and different level subrou-

tine nesting bit number. The following is a more

detailed description of the system architectures

of the four microcontrollers. Unless specified,

the architecture stated below exists in these

four microcontrollers.

Execution flow

The system clock is derived from either a crystal

or an RC oscillator. It is internally divided into

four non-overlapping clocks. Each instruction

cycle consists of four system clock cycles.

Instruction fetching and execution are pipe-

lined in such a way that a fetch takes one in-

struction cycle while decoding and execution

takes the next instruction cycle. The pipelining

scheme causes each instruction to effectively

execute in a cycle. If an instruction changes the

program counter, two cycles are required to

complete the instruction.

Program counter – PC

The program counter (PC) is of different sizes

ranging from 10 bits to 13 bits according to the

microcontroller selected (10 bits for the

HT48C10; 11 bits for the HT48C30; 12 bits for

the HT48C50; 13 bits for the HT48C70). It con-

trols a sequence in which the instructions

stored in the program ROM are executed. The

contents of the PC can specify 1024, 2048, 4096,

or 8192 addresses at maximum, according to

the microcontroller (HT48C10/HT48C30/

HT48C50/HT48C70) chosen.

After accessing a program memory word in or-

der to fetch an instruction code, the contents of

the PC is incremented by one. The PC then

points to the memory word consisting of the

next instruction code.

When executing a jump instruction, conditional

skip execution, loading a PCL register, a sub-

routine call, an initial reset, an internal inter-

rupt, an external interrupt, or returning from a

subroutine, the PC manipulates a program

transfer by loading the address corresponding

to each instruction.

The conditional skip is activated by instructions.

Once the condition is met, the next instruction,

fetched during the current instruction execution,

is discarded and a dummy cycle replaces it to get

a proper instruction; otherwise it proceeds to the

next instruction.

The lower byte of the PC (PCL) is a readable

and writeable register (06H). Moving data into

the PCL performs a short jump. The destination

is within 256 locations.

For a control transfer to take place, an addi-

tional dummy cycle is required.

Execution flow

HT48CXX/HT48RXX

25th May ’99

HT48C10 Datasheet(PDF) 13 Page - Holtek Semiconductor Inc

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