104 www.xilinx.com Virtex-4 FPGA Configuration User Guide
UG071 (v1.12) June 2, 2017
Chapter 8: Readback and Configuration Verification
Accessing Configuration Registers through the JTAG Interface
JTAG access to the Virtex-4 configuration logic is provided through the JTAG CFG_IN and
CFG_OUT registers. Note that the CFG_IN and CFG_OUT registers are not configuration
registers, rather they are JTAG registers like BYPASS and BOUNDARY_SCAN. Data
shifted in to the CFG_IN register go to the configuration packet processor, where they are
processed in the same way commands from the SelectMAP interface are processed.
Readback commands are written to the configuration logic by going through the CFG_IN
register; configuration memory is read through the CFG_OUT register. The JTAG state
transitions for accessing the CFG_IN and CFG_OUT registers are described in Table 8-3.
Configuration Register Read Procedure - JTAG
The simplest read operation targets a configuration register such as the COR or STAT
register. Any configuration register with read access can be read through the JTAG
interface, although not all registers offer read access. The procedure for reading the STAT
register through the JTAG interface follows:
1. Reset the TAP controller.
2. Shift the CFG_IN instruction into the JTAG Instruction Register through the Shift-IR
state. The LSB of the CFG_IN instruction is shifted first; the MSB is shifted while
moving the TAP controller out of the SHIFT-IR state.
3. Shift packet write commands into the CFG_IN register through the Shift-DR state:
a. Write the Synchronization word to the device.
b. Write one NOOP instruction to the device.
Table 8-3: Shifting in the JTAG CFG_IN and CFG_OUT Instructions
Step Description
Set and Hold # of
Clocks
(TCK)
TDI TMS
1
Clock five 1s on TMS to bring the device to the
TLR state
X15
2 Move into the RTI state X 0 1
3 Move into the Select-IR state X 1 2
4 Move into the Shift-IR State X 0 2
5
Shift the first 9 bits of the CFG_IN or CFG_OUT
instruction, LSB first
111000101
(CFG_IN)
09
111000100
(CFG_OUT)
6
Shift the MSB of the CFG_IN or CFG_OUT
instruction while exiting SHIFT-IR
111
7 Move into the SELECT-DR state X 1 2
8 Move into the SHIFT-DR state X 0 2
9
Shift data into the CFG_IN register or out of the
CFG_OUT register while in SHIFT_DR, MSB first.
X0X
10 Shift the LSB while exiting SHIFT-DR X 1 1
11 Reset the TAP by clocking five 1s on TMS X 1 5
To Next Page
Loading...
Need help?
General
