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AR# 10703

JTAG - How does the BSCAN_VIRTEX (BSCAN_SPARTAN2) block work?

描述

Keywords: BSCAN_VIRTEX, BSCAN_SPARTAN2, JTAG, user1, user2

How does the BSCAN_VIRTEX (BSCAN_SPARTAN2) block work? What kind of
signaling can be expected?

解决方案

Two resources should be read and understood first: the Libraries Guide entry about the
BSCAN_VIRTEX block, and the Virtex JTAG Application Note (Xilinx XAPP139, page 6).

However, these sources do not describe exactly how the various signals coming
from BSCAN_VIRTEX block actually toggle, and when. Below is a description and
waveform of the behavior.

(NOTE: All signals on the BSCAN_VIRTEX and BSCAN_SPARTAN2 blocks are
active-high signals.)

UPDATE: Active when the JTAG state machine is in the UPDATE-DR state.

SHIFT: Active when the JTAG state machine is in the SHIFT-DR state.

RESET: Active when the JTAG state machine is in the TEST-LOGIC-RESET state.

TDI: A mirror of the TDI pin. This port always has the TDI data reflected on it, and
whether or not it is appropriate for the USER scan chain.

SEL1: Indicates when the USER1 instruction has been loaded into the JTAG Instruction
Register. Becomes active in the UPDATE-IR state, and stays active until a new instruction
is loaded.

DRCK1: A mirror of the TCK pin when the USER1 instruction is loaded and the JTAG state
machine is in the SHIFT-DR state.

TDO1: Data input that is connected to the TDO pin when the USER1 instruction is loaded
and the JTAG state machine is in the SHIFT-DR state.

SEL2: The same as SEL1, except for the USER2 instruction.

DRCK2: The same as DRCK1, except for the USER2 instruction.

TDO2: The same as TDO1, except for the USER2 instruction.

 Figure 1 - Waveform of pertinent BSCAN_VIRTEX signals for the USER1 <br/>Scan Chain
Figure 1 - Waveform of pertinent BSCAN_VIRTEX signals for the USER1
Scan Chain

AR# 10703
日期 03/07/2007
状态 Active
Type ??????
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