UPSD3422 datasheet(39/293 Pages) STMICROELECTRONICS

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uPSD34xx

8032 addressing modes

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9.4

Immediate Addressing

This mode uses 8-bits of data (a constant) contained in the second byte of the instruction,

and stores it into the memory location or register indicated by the first byte of the instruction.

Thus, the data is immediately available within the instruction. This mode is commonly used

to initialize registers and SFRs or to perform mask operations.

There is also a 16-bit version of this mode for loading the DPTR Register. In this case, the

two bytes following the instruction byte contain the 16-bit value. For example:

9.5

External Direct Addressing

This mode will access external memory (XDATA) by using the 16-bit address stored in the

DPTR Register. There are only two instructions using this mode and both use the

accumulator to either receive a byte from external memory addressed by DPTR or to send a

byte from the accumulator to the address in DPTR. The uPSD34xx has a special feature to

alternate the contents (source and destination) of DPTR rapidly to implement very efficient

memory-to-memory transfers. For example:

Note:

See details in Section 11: Dual data pointers on page 47.

9.6

External Indirect Addressing

This mode will access external memory (XDATA) by using the 8-bit address stored in either

only 8-bits are available for address, this mode limits XDATA to a size of only 256 bytes (the

traditional Port 2 of the 8032 MCU is not available in the uPSD34xx, so it is not possible to

write the upper address byte).

For example:

Note:

This mode is not supported by uPSD34xx.

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

MOV A, 40#

; Move the constant, 40h, into

; the accumulator

MOV DPTR, 1234#

; Move the constant, 1234h, into

; DPTR

MOVX A, @DPTR

; Move contents of accumulator to

; XDATA at address contained in

; DPTR

MOVX @DPTR, A

; Move XDATA to accumulator

MOVX @R0,A

; Move into the accumulator the

; XDATA that is pointed to by

; the address contained in R0.

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