Xilinx UG129 manual Output Operations

OUTPUT Operations

R

		PicoBlaze Microcontroller
		IN_PORT[7:0] OUT_PORT[7:0]
	0 1	PORT_ID[7:0]
If performance is adequate,		READ_STROBE
remove the flip-flip and combine
the READ_STROBE and		WRITE_STROBE
PORT_ID decode logic.

	FIFO
READ	DATA_OUT	0 0
		S0
		S1
		READ_STROBE
		PORT_ID[1]
		PORT_ID[0]
		UG129_c6_04_060404
Figure 6-4:READ_STROBE Indicates a Successful INPUT Operation

OUTPUT Operations

As shown in Figure 6-5, an OUTPUT operation presents the contents of any of the 16 registers to the OUT_PORT output port. The PORT_ID output port, defined either by register sY or an 8-bit immediate constant, selects the desired output destination. The WRITE_STROBE output pulse indicates that data on the OUT_PORT port is valid and ready for capture. Typically, the WRITE_STROBE signal, combined with the decoded PORT_ID port, is used as either a clock enable or a write enable signal to other FPGA logic that captures the output data.

FPGA Logic

PicoBlaze Microcontroller

Register sX

8

OUT_PORT[7:0]

m
D	Q

WRITE_STROBE

EN

Register sY or Literal kk

8

PORT_ID[7:0]

n

UG129_c6_05_052004

Figure 6-5:OUTPUT Operation and FPGA Interface

The OUTPUT operation asserts the associated WRITE_STROBE output pulse beginning on rising CLK edge 1 of the two-cycle OUTPUT instruction , as shown in Figure 6-6. In this particular example, the PicoBlaze microcontroller writes the contents of register s0 to hexadecimal port address 65. The contents of register s0 appear on the OUT_PORT port; the port address appears on the PORT_ID port. The WRITE_STROBE goes High on the second clock cycle to indicate that data is valid.

PicoBlaze 8-bit Embedded Microcontroller www.xilinx.com 53

UG129 (v1.1.2) June 24, 2008