OR2C04A datasheet(52/192 Pages) ETC

52 / 192 page

Lucent Technologies Inc.

Data Sheet

ORCA Series 2 FPGAs

June 1999

Special Function Blocks

Special function blocks in the Series 2 provide extra

capabilities beyond general FPGA operation. These

blocks reside in the corners of the FPGA array.

Single Function Blocks

Most of the special function blocks perform a specific

dedicated function. These functions are data/configura-

tion readback control, global 3-state control (TS_ALL),

internal oscillator generation, global set/reset (GSRN),

and start-up logic.

Readback Logic

The readback logic is located in the upper right corner

of the FPGA.

Readback is used to read back the configuration data

and, optionally, the state of the PFU outputs. A read-

back operation can be done while the FPGA is in nor-

mal system operation. The readback operation cannot

be daisy-chained. To use readback, the user selects

options in the bit stream generator in the

ORCA

Foundry Development System.

Table 11 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 11. Readback Options

The pins used for readback are readback data

(RD_DATA), read configuration (RD_CFG), and configu-

ration clock (CCLK). A readback operation is initiated

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 ris-

ing 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 ris-

ing edge of CCLK after RD_CFG is input low (see Table

48, Readback Timing Characteristics in the Timing

Characteristics section).

It should be noted that the RD_DATA output pin is also

used as the dedicated boundary-scan output pin, TDO.

If this pin is being used as TDO, the RD_DATA output

from readback can be routed internally to any other pin

desired. The RD_CFG input pin is also used to control

the global 3-state (TS_ALL) function. Before and during

configuration, the TS_ALL signal is always driven by

the RD_CFG input and readback is disabled. After con-

figuration, the selection as to whether this input drives

the readback or global 3-state function is determined

by a set of bit stream options. If used as the RD_CFG

input for readback, the internal TS_ALL input can be

routed internally to be driven by any input pin.

The readback frame contains the configuration data

and the state of the internal logic. During readback, the

value of all five PFU outputs can be captured. The fol-

lowing options are allowed when doing a capture of the

PFU outputs.

1. Do not capture data (the data written to the capture

RAMs, usually 0, will be read back).

2. Capture data upon entering readback.

3. Capture data based upon a configurable signal

internal to the FPGA. If this signal is tied to

logic 0, capture RAMs are written continuously.

4. Capture data on either options 2 or 3 above.

The readback frame has a similar, but not identical, for-

mat to the configuration frame. This eases a bitwise

comparison between the configuration and readback

data. The readback data is not inverted. Every data

frame has one low start bit and one high stop bit. The

preamble, including the length count field, is not part of

the readback frame. The readback frame contains

states in locations not used in the configuration. These

locations need to be masked out when comparing the

configuration and readback frames. The development

system optionally provides a readback bit stream to

compare to readback from the FPGA. Also note that if

any of the LUTs are used as RAM and new data is writ-

ten to them, these bits will not have the same values as

the original configuration data frame either.

Option

Function

Prohibit Readback

Allow One Readback Only

Allow Unrestricted Number of Readbacks

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