XC2S50 Xilinx, Inc., XC2S50 Datasheet - Page 25

• Manufacturer Part Number: XC2S50
• Description: Spartan-II 2.5V FPGA Family
• Manufacturer: Xilinx, Inc.

Spartan-II 2.5V FPGA Family: Functional Description
If CCLK is slower than F
BUSY. In this case, the above handshake is unnecessary,
and data can simply be entered into the FPGA every CCLK
cycle.
A configuration packet does not have to be written in one
continuous stretch, rather it can be split into many write
sequences. Each sequence would involve assertion of CS.
In applications where multiple clock cycles may be required
to access the configuration data before each byte can be
loaded into the Slave Parallel interface, a new byte of data
may not be ready for each consecutive CCLK edge. In such
Module 2 of 4
18
Figure 18: Loading Configuration Data for the Slave
CCLK Rising Edge
WRITE and CS
WRITE and CS
To CRC Check
Byte on Next
Configuration
Driving BUSY
Configuration
User Drives
User Drives
Goes High
Load One
After INIT
Data File?
Parallel Mode
End of
FPGA
High?
High
Low
CCNH
No
Yes
, the FPGA will never assert
Yes
No
DS001_19_032300
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1-800-255-7778
a case the CS signal may be de-asserted until the next byte
is valid on D0-D7. While CS is High, the Slave Parallel inter-
face does not expect any data and ignores all CCLK transi-
tions. However, to avoid aborting configuration, WRITE
must continue to be asserted while CS is asserted.
Abort
To abort configuration during a write sequence, de-assert
WRITE while holding CS Low. The abort operation is initi-
ated at the rising edge of CCLK, as shown in
page
operation is complete. After aborting configuration, data is
assumed to be unaligned to word boundaries and the FPGA
requires a new synchronization word prior to accepting any
new packets.
Boundary-Scan Mode
In the boundary-scan mode, no nondedicated pins are
required, configuration being done entirely through the
IEEE 1149.1 Test Access Port.
Configuration through the TAP uses the special CFG_IN
instruction. This instruction allows data input on TDI to be
converted into data packets for the internal configuration
bus.
The following steps are required to configure the FPGA
through the boundary-scan port.
1. Load the CFG_IN instruction into the boundary-scan
2. Enter the Shift-DR (SDR) state
3. Shift a standard configuration bitstream into TDI
4. Return to Run-Test-Idle (RTI)
5. Load the JSTART instruction into IR
6. Enter the SDR state
7. Clock TCK through the sequence (the length is
8. Return to RTI
Configuration and readback via the TAP is always available.
The boundary-scan mode simply locks out the other modes.
The boundary-scan mode is selected by a <10x> on the
mode pins (M0, M1, M2).
Readback
The configuration data stored in the Spartan-II configuration
memory can be readback for verification. Along with the
configuration data it is possible to readback the contents of
all flip-flops/latches, LUT RAMs, and block RAMs. This
capability is used for real-time debugging.
For more detailed information see XAPP176, Spartan-II
FPGA Family Configuration and Readback.
instruction register (IR)
programmable)
19. The device will remain BUSY until the aborted
DS001-2 (v2.2) September 3, 2003
Product Specification
Figure 20,
R