OR4E2 datasheet(46/124 Pages) AGERE

46 / 124 page

Lucent Technologies Inc.

Preliminary Data Sheet

December 2000

ORCA Series 4 FPGAs

Special Function Blocks (continued)

5-5971(F)

Figure 30. Instruction Register Scan Timing Diagram

TCK

TMS

TDI

Readback Logic

The readback logic can be enabled via a bit stream

option or by instantiation of a library readback compo-

nent.

Readback is used to read back the configuration data

and, optionally, the state of all PFU and PIO FF out-

puts. A readback operation can be done while the

FPGA is in normal system operation. The readback

operation can be daisy-chained. To use readback, the

user selects options in the bit stream generator in the

ORCA Foundry development system.

Table 25 provides readback options selected in the bit

stream generator tool. The table provides the number

of times that the configuration data can be read back.

This is intended primarily to give the user control over

the security of the FPGA’s configuration program. The

user can prohibit readback (0), allow a single readback

(1), or allow unrestricted readback (U).

Table 25. Readback Options

Readback can be performed via the Series 4 MPI or by

using dedicated FPGA readback controls. If the MPI is

enabled, readback via the dedicated FPGA readback

logic is disabled. Readback using the MPI is discussed

in the MPI section.

The pins used for dedicated readback are readback

data (RD_DATA), read configuration (RD_CFG), and

configuration clock (CCLK). A readback operation is ini-

tiated by a high-to-low transition on RD_CFG. The

RD_CFG

input must remain low during the readback

operation. The readback operation can be restarted at

frame 0 by driving the RD_CFG pin high, applying at

least two rising edges of CCLK, and then driving

RD_CFG

low again. One bit of data is shifted out on

RD_DATA at the rising edge of CCLK. The first start bit

of the readback frame is transmitted out several cycles

after the first rising edge of CCLK after RD_CFG is input

low (see the readback timing characteristics table in the

timing characteristics section). To be certain of the start

of the readback frame, the data can be monitored for

the 01 frame start bit pair.

Option

Function

Prohibit Readback

Allow One Readback Only

Allow Unrestricted Number of Readbacks

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