UPD7554AA 데이터 시트보기 (PDF) - NEC => Renesas Technology

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UPD7554AA

4-BIT SINGLE-CHIP MICROCOMPUTER

NEC => Renesas Technology 

µPD7554A, 7554A(A)

2.5 DATA MEMORY (RAM): 64 × 4 BITS

The data memory is a static RAM of 64 word × 4 bits configuration. It is used as the area to store or stack processed

data. The data memory may be processed in 8-bit units when paired with the accumulator.

Fig. 2-6 Data Memory Map

( 0 ) 00H

64 Words × 4 Bits

(63) 3FH

The data memory is addressed in the following three ways:

• Direct: Direct addressing based on immediate data of an instruction

• Register indirect: Indirect addressing according to the contents of the pair register HL (including automatic

incrementation and decrementation)

• Stack: Indirect addressing according to the contents of the stack pointer (SP)

An arbitrary space of the data memory is available as stack memory. The boundary of the stack area is specified

when the TAMSP instruction initializes the SP. After that, the stack area is accessed automatically by the call or return

instruction.

After the call instruction is executed, the content of the PC and PSW is stored in the order shown in the following

diagram:

Stack Area

3

0

SP – 4

0

0 PC9 PC8

SP – 3

PSWNote

SP – 2

PC3 – PC0

SP – 1

PC7 – PC4

Note Bit 1 is fixed at 0.

When the return instruction is executed, the content of the PSW is not restored while those of the PC are restored.

Data in the data memory is retained at a low supply voltage in the STOP mode.

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