UPD75236GJ View Datasheet(PDF) - NEC => Renesas Technology

Part Name

Description

Manufacturer

UPD75236GJ

4-BIT SINGLE-CHIP MICROCOMPUTER

NEC => Renesas Technology 

µPD75236

3.5 ACCUMULATOR

In the µPD75236, A register and XA register pair function as an accumulator. The 4-bit data processing

instruction is executed mainly by A register and the 8-bit data processing instruction is executed mainly by XA

register pair.

For execution of the bit manipulation instruction, the carry flag (CY) functions as a bit accumulator.

Fig. 3-7 Accumulator

CY

Bit Accumulator

A

4-Bit Accumulator

X

A

8-Bit Accumulator

3.6 STACK POINTER (SP) AND STACK BANK SELECT REGISTER (SBS)

In the µPD75236, the static RAM is used as a static memory (LIFO type) and the 8-bit register which holds

the start address information in the stack area is a stack pointer (SP).

The stack area is located at addresses 000H to 2FFH of memory banks 0, 1 and 2. Specify one memory bank

by a 2-bit SBS.

The SP is decremented prior to a write (save) to the stack memory and incremented after a read (restore)

from the stack memory. Set SBS by the 4-bit memory manipulation instruction. In this case, set the higher 2-

bits to 00.

The data to be saved/restored by each stack operation is shown in Figs. 3-9 and 3-10.

The SP initial value is set by the 8-bit memory manipulation instruction and the SBS initial value is set by

the 4-bit memory manipulation instruction and then the stack area is determined. The SP and SBS contents can

also be read.

Table 3-1 Stack Areas to be Selected by SBS

SBS

SBS1

SBS0

0

0

0

1

1

0

1

1

Stack Area

Memory bank 0

Memory bank 1

Memory bank 2

Setting disabled

When the SP initial value is set to 00H, stack starts with the most significant address (nFFH) of the memory

bank (n: n = 0, 1, 2) specified by SBS.

The stack area is limited to the memory bank specified by SBS. When stack operation is further carried out

at address n00H, the address is reset to nFFH in the same bank. Linear stack past the memory bank boundary is

not possible without rewriting SBS.

Since RESET input makes the SP and SBS undefined, be sure to initialize the SP and SBS to any desired

value at the beginning of the program.

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