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OR2C04A

ORCA® Series 2 Field-Programmable Gate Arrays

Lattice Semiconductor 

Data Sheet

January 2002

ORCA Series 2 FPGAs

FPGA Configuration Modes (continued)

Asynchronous Peripheral Mode

Figure 42 shows the connections needed for the asyn-

chronous peripheral mode. In this mode, the FPGA

system interface is similar to that of a microprocessor-

peripheral interface. The microprocessor generates the

control signals to write an 8-bit byte into the FPGA. The

FPGA control inputs include active-low CS0 and active-

high CS1 chip selects, a write WR input, and a read RD

input. The chip selects can be cycled or maintained at a

static level during the configuration cycle. Each byte of

data is written into the FPGA’s D[7:0] input pins.

The FPGA provides a RDY status output to indicate

that another byte can be loaded. A low on RDY indi-

cates that the double-buffered hold/shift registers are

not ready to receive data, and this pin must be moni-

tored to go high before another byte of data can be

written. The shortest time RDY is low occurs when a

byte is loaded into the hold register and the shift regis-

ter is empty, in which case the byte is immediately

transferred to the shift register. The longest time for

RDY to remain low occurs when a byte is loaded into

the holding register and the shift register has just

started shifting configuration data into configuration

RAM.

The RDY status is also available on the D7 pin by

enabling the chip selects, setting WR high, and apply-

ing RD low, where the RD input is an output enable for

the D7 pin when RD is low. The D[6:0] pins are not

enabled to drive when RD is low and, thus, only act as

input pins in asynchronous peripheral mode.

8

MICRO-

PROCESSOR

ADDRESS

DECODE LOGIC

DOUT

PRGM

D[7:0] CCLK

RDY/BUSY

INIT

DONE

CS0

ORCA

SERIES

CS1 FPGA

TO DAISY-

CHAINED

DEVICES

BUS

RD

CONTROLLER

WR

VDD

M2

M1

M0

HDC

LDC

5-4484(F)

Figure 42. Asynchronous Peripheral Configuration

Schematic

Synchronous Peripheral Mode

In the synchronous peripheral mode, byte-wide data is

input into D[7:0] on the rising edge of the CCLK input.

The first data byte is clocked in on the second CCLK

after INIT goes high. Subsequent data bytes are

clocked in on every eighth rising edge of CCLK. The

RDY signal is an output which acts as an acknowledge.

RDY goes high one CCLK after data is clocked and,

after one CCLK cycle, returns low. The process repeats

until all of the data is loaded into the FPGA. The data

begins shifting on DOUT 1.5 cycles after it is loaded in

parallel. It requires additional CCLKs after the last byte

is loaded to complete the shifting. Figure 43 shows the

connections for synchronous peripheral mode.

As with master modes, the peripheral modes can be

used as the lead FPGA for a daisy chain of slave

FPGAs.

8

MICRO-

PROCESSOR

PRGM

D[7:0]

DOUT

ORCA

SERIES

FPGA

CCLK

RDY/BUSY

INIT

TO DAISY-

CHAINED

DEVICES

+5 V

M2

HDC

M1

M0

LDC

5-4486(F)

Figure 43. Synchronous Peripheral Configuration

Schematic

Lattice Semiconductor

49

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