User guide

100 www.xilinx.com Spartan-6 FPGA Configuration User Guide
UG380 (v2.7) October 29, 2014
Chapter 5: Configuration Details
CBC_REG Register
This register is used by the bitstream compression option to hold the Initial Vector (IV) for
AES decryption.
IDCODE Register
Any writes to the FDRI register must be preceded by a write to this register. The provided
IDCODE must match the device’s IDCODE. See Configuration Sequence, page 80.
A read of this register returns the device IDCODE.
CSBO Register
The CSBO register is designed to assert the CSB_O signal and then ignore any incoming
data for a specified word count. It works much the same way as the LOUT register except
that it only outputs a Low on CSB_O and no data is passed through. Like the LOUT
register, multiple calls can be nested for different devices in support of daisy-chaining.
Command Register (CMD)
The Command Register is used to instruct the configuration control logic to strobe global
signals and perform other configuration functions. The command present in the CMD
register is executed each time the FAR is loaded with a new value. Table 5-33 lists the
Command Register commands and codes.
Table 5-33: Command Register Codes
Command Code Description
NULL 00000 Null Command
WCFG 00001 Writes Configuration Data: Used prior to writing configuration
data to the FDRI.
MFW 00010 Multiple Frame Write: Used to perform a write of a single frame
data to multiple frame addresses.
LFRM 00011 Last Frame: Deasserts the GHIGH_B signal, activating all
interconnects. The GHIGH_B signal is asserted with the AGHIGH
command.
RCFG 00100 Reads Configuration Data: Used prior to reading configuration
data from the FDRO.
START 00101 Begins the Startup Sequence: Initiates the startup sequence. The
startup sequence begins after a successful CRC check and a
DESYNC command are performed.
RCRC 00111 Resets CRC: Resets the CRC register.
AGHIGH 01000 Asserts the GHIGH_B signal: Places all interconnect in a high-Z
state to prevent contention when writing new configuration data.
This command is only used in shutdown reconfiguration.
Interconnect is reactivated with the LFRM command.
GRESTORE 01010 Pulses the GRESTORE signal: Sets/resets (depending on user
configuration) IOB and CLB flip-flops.