Data Sheet
June 1999
ORCA Series 3C and 3T FPGAs
FPGA Configuration Modes (continued)
Daisy-Chaining with Boundary Scan
Multiple FPGAs can be configured through the JTAG ports by using a daisy-chain of the FPGAs. This daisy-chain-
ing operation is available upon initial configuration after powerup, after a power-on reset, after pulling the program
pin to reset the chip, or during a reconfiguration if the EN_JTAG RAM has been set.
All daisy-chained FPGAs are connected in series. Each FPGA reads and shifts the preamble and length count in
on the positive TCK and out on the negative TCK edges.
An upstream FPGA that has received the preamble and length count outputs a high on TDO until it has received
the appropriate number of data frames so that downstream FPGAs do not receive frame start bit pairs. After load-
ing and retransmitting the preamble and length count to a daisy-chain of downstream devices, the lead device
loads its configuration data frames.
The loading of configuration data continues after the lead device had received its configuration read into TDI of
downstream devices on the positive edge of TCK, and shifted out TDO on the negative edge of TCK. Figure 63
shows the connections for loading multiple FPGAs in a JTAG daisy-chain configuration.
Lucent Technologies Inc.
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AGERE [ AGERE SYSTEMS ]
