Xilinx UG129 manual Moving Data, Program Flow Control

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Chapter 3: PicoBlaze Instruction Set

Moving Data

Data movement between various resources is an essential microcontroller function.

Figure 3-26shows the various PicoBlaze instructions to move data.

IN_PORT

Scratchpad RAM

STORE		FETCH
	Registers
	LOAD sX, sY
INPUT			OUTPUT

OUT_PORT

LOAD sX, kk	INPUT sX, (sY)
	OUTPUT sX, (sY)

Instruction

Store

INPUT sX, kk OUTPUT sX, kk

PORT_ID

UG129_c3_05_060404

Figure 3-26:Data Movement Instructions

The LOAD sX,sY instruction moves data between two PicoBlaze registers; Register sX receives the data. The LOAD sX,kk instruction loads an immediate byte-wide constant into the specified register. See also “LOAD sX, Operand — Load Register sX with Operand,” page 102. The LOAD instructions do not affect the CARRY or ZERO flags.

The STORE and FETCH instructions move data between the register file and the scratchpad RAM. See “Chapter 5, “Scratchpad RAM,” for more information.

During an INPUT operation, data from the IN_PORT input port is always read to one of the registers. Likewise, during an OUTPUT instruction, data written to the OUT_PORT output port always originates from one of the registers. The input/output address, provided on the PORT_ID output, originates either from one of the registers or as a literal constant from the instruction store. See Chapter 6, “Input and Output Ports,” for more information.

Program Flow Control

The Program Counter (PC) points to the next instruction to be executed and directly controls the PicoBlaze program flow. By default, the PicoBlaze microcontroller proceeds to the next instruction in the instruction store (PC=PC+1). The PC cannot be directly accessed. However, three different PicoBlaze instructions, JUMP and the CALL/RETURN pair potentially modify the default program flow by loading the PC with a different value. An enabled interrupt event also modifies program flow but this case is described in Chapter 4, “Interrupts.” Likewise, a Reset Event resets the PC to zero, restarting program execution.

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		UG129 (v1.1.2) June 24, 2008