OR4 datasheet(39/152 Pages) LATTICE

39 / 152 page

Data Sheet

May, 2006

Lattice Semiconductor

ORCA Series 4 FPGAs

Programmable Input/Output Cells

(continued)

0204(F).

Figure 24. PIO Shift Register

PIO

SHIFT REGISTER

OUT FROM FPGA

SHIFT REGISTER

INTO FPGA

CLK

Special Function Blocks

Special function blocks in the Series 4 provide extra

capabilities beyond general FPGA operation. These

blocks reside in the corners and MIDs (middle inter-

quad areas) of the FPGA array.

Internal Oscillator

The internal oscillator resides in the upper left corner of

the FPGA array. It has output clock frequencies of

1.25 MHz and 10 MHz. The internal oscillator is the

source of the internal CCLK used for conﬁguration. It

may also be used after conﬁguration as a general-

purpose clock signal.

Global Set/Reset (GSRN)

The GSRN logic resides in the upper-left corner of the

FPGA. GSRN is an invertible, default, active-low signal

that is used to reset all of the user-accessible latches/

FFs on the device. GSRN is automatically asserted at

powerup and during conﬁguration of the device.

The timing of the release of GSRN at the end of conﬁg-

uration can be programmed in the start-up logic

described below. Following conﬁguration, GSRN may

be connected to the RESET pin via dedicated routing, or

it may be connected to any signal via normal routing.

GSRN can also be controlled via a system bus register

command. Within each PFU and PIO, individual FFs

and latches can be programmed to either be set or

reset when GSRN is asserted. Series 4 allows individ-

ual PFUs and PIOs to turn off the GSRN signal to its

latches/FFs after conﬁguration.

The RESET input pad has a special relationship to

GSRN. During conﬁguration, the RESET input pad

always initiates a conﬁguration abort, as described in

the FPGA States of Operation section. After conﬁgura-

tion, the GSRN can either be disabled (the default),

directly connected to the RESET input pad, or sourced

by a lower-right corner signal. If the RESET input pad is

not used as a global reset after conﬁguration, this pad

can be used as a normal input pad.

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