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OR2C04A

ORCA® Series 2 Field-Programmable Gate Arrays

Lattice Semiconductor 

ORCA Series 2 FPGAs

Data Sheet

January 2002

FPGA States of Operation

Prior to becoming operational, the FPGA goes through a

sequence of states, including initialization, configuration,

and start-up. Figure 36 outlines these three FPGA

states.

POWERUP

– POWER-ON TIME DELAY

INITIALIZATION

– CLEAR CONFIGURATION MEMORY

– INIT LOW, HDC HIGH, LDC LOW

YES

BIT

ERROR

NO

RESET,

INIT,

OR

PRGM

LOW

NO

YES

CONFIGURATION

– M[3:0] MODE IS SELECTED

– CONFIGURATION DATA FRAME WRITTEN

– INIT HIGH, HDC HIGH, LDC LOW

– DOUT ACTIVE

RESET

OR

PRGM

LOW

START-UP

– ACTIVE I/O

– RELEASE INTERNAL RESET

– DONE GOES HIGH

PRGM

LOW

OPERATION

5-4529(F).r6

Figure 36. FPGA States of Operation

Initialization

Upon powerup, the device goes through an initialization

process. First, an internal power-on-reset circuit is trig-

gered when power is applied. When VDD reaches the

voltage at which portions of the FPGA begin to operate

(2.5 V to 3 V for the OR2CxxA, 2.2 V to 2.7 V for the

OR2TxxA/OR2TxxB), the I/Os are configured based on

the configuration mode, as determined by the mode

select inputs M[2:0]. A time-out delay is initiated when

VDD reaches between 3.0 V and 4.0 V (OR2CxxA) or

2.7 V to 3.0 V (OR2TxxA/2TxxB) to allow the power

supply voltage to stabilize. The INIT and DONE outputs

are low. At powerup, if VDD does not rise from 2.0 V to

VDD in less than 25 ms, the user should delay configu-

ration by inputting a low into INIT, PRGM, or RESET

until VDD is greater than the recommended minimum

operating voltage (4.75 V for OR2CxxA commercial

devices and 3.0 V for OR2TxxA/B devices).

At the end of initialization, the default configuration

option is that the configuration RAM is written to a low

state. This prevents shorts prior to configuration. As a

configuration option, after the first configuration (i.e., at

reconfiguration), the user can reconfigure without

clearing the internal configuration RAM first.

The active-low, open-drain initialization signal INIT is

released and must be pulled high by an external resis-

tor when initialization is complete. To synchronize the

configuration of multiple FPGAs, one or more INIT pins

should be wire-ANDed. If INIT is held low by one or

more FPGAs or an external device, the FPGA remains

in the initialization state. INIT can be used to signal that

the FPGAs are not yet initialized. After INIT goes high

for two internal clock cycles, the mode lines (M[3:0])

are sampled and the FPGA enters the configuration

state.

The high during configuration (HDC), low during config-

uration (LDC), and DONE signals are active outputs in

the FPGA’s initialization and configuration states. HDC,

LDC, and DONE can be used to provide control of

external logic signals such as reset, bus enable, or

PROM enable during configuration. For parallel master

configuration modes, these signals provide PROM

enable control and allow the data pins to be shared

with user logic signals.

If configuration has begun, an assertion of RESET or

PRGM initiates an abort, returning the FPGA to the ini-

tialization state. The PRGM and RESET pins must be

pulled back high before the FPGA will enter the config-

uration state. During the start-up and operating states,

only the assertion of PRGM causes a reconfiguration.

In the master configuration modes, the FPGA is the

source of configuration clock (CCLK). In this mode, the

initialization state is extended to ensure that, in daisy-

chain operation, all daisy-chained slave devices are

ready. Independent of differences in clock rates, master

mode devices remain in the initialization state an addi-

tional six internal clock cycles after INIT goes high.

When configuration is initiated, a counter in the FPGA

is set to 0 and begins to count configuration clock

cycles applied to the FPGA. As each configuration data

frame is supplied to the FPGA, it is internally assem-

bled into data words. Each data word is loaded into the

internal configuration memory. The configuration load-

ing process is complete when the internal length count

equals the loaded length count in the length count field,

and the required end of configuration frame is written.

40

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