User guide

84 www.xilinx.com Spartan-6 FPGA Configuration User Guide
UG380 (v2.7) October 29, 2014
Chapter 5: Configuration Details
Bitstream Loading (Steps 4-7)
The bitstream loading process is similar for all configuration modes; the primary
difference between modes is the interface to the configuration logic. Details on the different
configuration interfaces are provided in Chapter 2, Configuration Interface Basics.
Synchronization (Step 4)
The synchronization word alerts the device to upcoming configuration data and aligns the
configuration data with the internal configuration logic. Any data on the configuration
input pins prior to synchronization is ignored.
Synchronization is transparent to most users because all configuration bitstreams (BIT
files) generated by the BitGen software include both the bus width detection
pattern/synchronization word.
Check Device ID (Step 5)
After the device is synchronized, a device ID check must pass before the configuration data
frames can be loaded. This prevents a configuration with a bitstream that is formatted for
a different device. For example, the device ID check should prevent an XC6SLX4 from
being configured with an XC6SLX9 bitstream.
The device ID check is built into the bitstream, making this step transparent to most
designers. Table 5-14 shows the signals relating to the device ID check. The device ID check
is performed through commands in the bitstream to the configuration logic, not through
the JTAG IDCODE register in this case.
X-Ref Target - Figure 5-7
Figure 5-7: Synchronization (Step 4)
Device
Power-Up
Sample Mode
Pins
Synchronization
Device ID
Check
CRC Check
Clear
Configuration
Memory
Startup
Sequence
Load
Configuration
Data
Start
Finish
UG380_c5_07_042909
Bitstream
Loading
Steps
123 45678
X-Ref Target - Figure 5-8
Figure 5-8: Check Device ID (Step 5)
Device
Power-Up
Sample Mode
Pins
Synchronization
Device ID
Check
CRC Check
Clear
Configuration
Memory
Startup
Sequence
Load
Configuration
Data
Start
Finish
UG380_c5_08_042909
Bitstream
Loading
Steps
123 45678