W742E816 Просмотр технического описания (PDF) - Winbond

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W742E816

4-BIT MICROCONTROLLER

Winbond 

W742E/C816

Deleted: SA5505

Deleted: W742C811

5.2 Stack Register (STACK)

The stack register is organized as 53 bits x 16 levels (first-in, last-out). When either a call subroutine

or an interrupt is executed, the program counter (PC), TAB0, TAB1, TAB2, TAB3, DBKRL, DBKRH,

WRP, ROMPR, PAGE, ACC and CF will be pushed into the stack register automatically. At the end of

a call subroutine or an interrupt service subroutine, the RTN (only restore the program counter) and

RTN #I instruction could pop the contents of the stack register into the corresponding registers. It can

restore part of contents of stack buffer. When the stack register is pushed over the 16th level, the

contents of the first level will be overwritten. In the other words, the stack register is always 16 levels

deep. The bit definition of #I is listed below.

I = 0000 0000

Bit0 = 1

Bit1 = 1

Bit2 = 1

Bit3 = 1

Bit4 = 1

Bit5 = 1

Bit6 = 1

Pop PC from stack only

Pop TAB0, TAB1, TAB2, TAB3 from stack

Pop DBKRL, DBKRH from stack

Pop WRP from stack

Pop ROMPR from stack

Pop PAGE from stack

Pop ACC from stack

Pop CF from stack

5.3 Program Memory (ROM)

The read-only memory (ROM) is used to store program codes or the look-up table that can be

arranged up to 65536(64K) × 4 bits. The program ROM is divided into sixteen pages; the size of each

page is 2048(2K) × 16 bits. So the total ROM size is 32768(32K) × 16 bits. Before the jump or

subroutine call instructions are to be executed, the destination ROM page register (ROMPR) must be

determined firstly. The ROM page can be selected by executing the MOV ROMPR, #I or MOV

ROMPR, RAM instructions. But the branch decision instructions (e.g. JB0, SKB0, JZ, JC, ...) must

jump into the same ROM page. The look-up table area is allocated in lower half part of ROM (PC:

4000H to 7FFFH). Each look-up table element is composed of 4 bits, so the look-up table can be

addressed up to 65536(64K) elements. It uses instructions MOV TAB0, R MOV TAB1, R MOV TAB2,

R MOV TAB3, R to determine the look-up table element address. The look-up table address is 4 times

PC counter, and the offset value is 4000H. Instruction MOVC R is used to read the look-up table

content and save data into the RAM. The organization of the program memory is shown in Figure 5-1.

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