
42
Lucent Technologies Inc.
Data Sheet
June 1999
ORCA Series 2 FPGAs
FPGA States of Operation 
(continued)
Start-Up
After configuration, the FPGA enters the start-up 
phase. This phase is the transition between the config-
uration and operational states and begins when the 
number of CCLKs received after 
INIT
 goes high is equal 
to the value of the length count field in the configuration 
frame and when the end of configuration frame has 
been written. The system design issue in the start-up 
phase is to ensure the user I/Os become active without 
inadvertently activating devices in the system or caus-
ing bus contention. A second system design concern is 
the timing of the release of global set/reset of the PLC 
latches/FFs. 
There are configuration options that control the relative 
timing of three events: DONE going high, release of the 
set/reset of internal FFs, and user I/Os becoming 
active. Figure 38 shows the start-up timing for both the 
ORCA and ATT3000 Series FPGAs. The system 
designer determines the relative timing of the I/Os 
becoming active, DONE going high, and the release of 
the set/reset of internal FFs. In the ORCA Series 
FPGA, the three events can occur in any arbitrary 
sequence. This means that they can occur before or 
after each other, or they can occur simultaneously. 
There are four main start-up modes: CCLK_NOSYNC, 
CCLK_SYNC, UCLK_NOSYNC, and UCLK_SYNC. 
The only difference between the modes starting with 
CCLK and those starting with UCLK is that for the 
UCLK modes, a user clock must be supplied to the 
start-up logic. The timing of start-up events is then 
based upon this user clock, rather than CCLK. The dif-
ference between the SYNC and NOSYNC modes is 
that, for SYNC mode, the timing of two of the start-up 
events (release of the set/reset of internal FFs and the 
I/Os becoming active) is triggered by the rise of the 
external DONE pin followed by a variable number of ris-
ing clock edges (either CCLK or UCLK). For the 
NOSYNC mode, the timing of these two events is 
based only on either CCLK or UCLK.
DONE is an open-drain bidirectional pin that may 
include an optional (enabled by default) pull-up resistor 
to accommodate wired ANDing. The open-drain DONE 
signals from multiple FPGAs can be tied together 
(ANDed) with a pull-up (internal or external) and used 
as an active-high ready signal, an active-low PROM 
enable, or a reset to other portions of the system. 
When used in SYNC mode, these ANDed DONE pins 
can be used to synchronize the other two start-up 
events, since they can all be synchronized to the same 
external signal. This signal will not rise until all FPGAs 
release their DONE pins, allowing the signal to be 
pulled high.
The default for ORCAis the CCLK_SYNC synchro-
nized start-up mode where DONE is released on the 
first CCLK rising edge, C1 (see Figure 38). Since this is 
a synchronized start-up mode, the open-drain DONE 
signal can be held low externally to stop the occurrence 
of the other two start-up events. Once the DONE pin 
has been released and pulled up to a high level, the 
other two start-up events can be programmed individu-
ally to either happen immediately or after up to four ris-
ing edges of CCLK (Di, Di + 1, Di + 2, Di + 3, Di + 4). 
The default is for both events to happen immediately 
after DONE is released and pulled high.
A commonly used design technique is to release 
DONE one or more clock cycles before allowing the I/O 
to become active. This allows other configuration 
devices, such as PROMs, to be disconnected using the 
DONE signal so that there is no bus contention when 
the I/Os become active. In addition to controlling the 
FPGA during start-up, other start-up techniques that 
avoid contention include using isolation devices 
between the FPGA and other circuits in the system, 
reassigning I/O locations and maintaining I/Os as 
3-stated outputs until contentions are resolved.
Each of these start-up options can be selected during 
bit stream generation in ORCAFoundry, using 
Advanced Options. For more information, please see 
the ORCA Foundry documentation.
Reconfiguration
To reconfigure the FPGA when the device is operating 
in the system, a low pulse is input into 
PRGM
. The con-
figuration data in the FPGA is cleared, and the I/Os not 
used for configuration are 3-stated. The FPGA then 
samples the mode select inputs and begins reconfigu-
ration. When reconfiguration is complete, DONE is 
released, allowing it to be pulled high.