UPSD3312D datasheet(48/272 Pages) STMICROELECTRONICS

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8032 addressing modes

UPSD33xx

48/272

Doc ID 9685 Rev 7

9.7

Indexed addressing

This mode is used for the MOVC instruction which allows the 8032 to read a constant from

program memory (not data memory). MOVC is often used to read look-up tables that are

embedded in program memory. The final address produced by this mode is the result of

adding either the 16-bit PC or DPTR value to the contents of the accumulator. The value in

the accumulator is referred to as an index. The data fetched from the final location in

program memory is stored into the accumulator, overwriting the index value that was

previously stored there. For example:

9.8

Relative addressing

This mode will add the two’s-compliment number stored in the second byte of the instruction

to the program counter for short jumps within +128 or –127 addresses relative to the

program counter. This is commonly used for looping and is very efficient since no additional

bus cycle is needed to fetch the jump destination address. For example:

9.9

Absolute addressing

This mode will append the 5 high-order bits of the address of the next instruction to the 11

low-order bits of an ACALL or AJUMP instruction to produce a 16-bit jump address. The

jump will be within the same 2 Kbyte page of program memory as the first byte of the

following instruction. For example:

MOVX @R0,A

; Move into the accumulator the

; XDATA that is pointed to by

; the address contained in R0.

MOVC A, @A+DPTR

; Move code byte relative to

; DPTR into accumulator

MOVC A, @A+PC

; Move code byte relative to PC

; into accumulator

SJMP 34h

; Jump 34h bytes ahead (in program

; memory) of the address at which

; the SJMP instruction is stored. If

; SJMP is at 1000h, program

; execution jumps to 1034h.

AJMP 0500h

; If next instruction is located at

; address 4000h, the resulting jump

; will be made to 4500h.

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