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Data Sheet
September, 2002
Lattice Semiconductor
39
ORCA Series 4 FPGAs
Programmable Input/Output Cells
(continued)
0204(F).
Figure 24. PIO Shift Register
INDD
OUTSH
OUTDD
PIO
INDD
OUTSH
OUTDD
PIO
INDD
OUTSH
OUTDD
PIO
INDD
OUTSH
OUTDD
PIO
SHIFT REGISTER
OUT FROM FPGA
SHIFT REGISTER
INTO FPGA
CLK
OUTSH1
OUTSH2
OUTSH3
OUTSH4
INSH1
INTSH2
INSH3
INSH4
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 conguration. It
may also be used after conguration 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 conguration of the device.
The timing of the release of GSRN at the end of cong-
uration can be programmed in the start-up logic
described below. Following conguration, 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 conguration.
The RESET input pad has a special relationship to
GSRN. During conguration, the RESET input pad
always initiates a conguration abort, as described in
the FPGA States of Operation section. After congura-
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 conguration, this pad
can be used as a normal input pad.