Answers Database Cable - How many devices can Parallel III (JTAG) cable program in a chain? Record #1272 Product Family: Hardware Product Line: Other Product Part: Parallel Download Cable Problem Title: Cable - How many devices can Parallel III (JTAG) cable program in a chain? Problem Description: Urgency: Standard General Description: How many devices can Parallel III (JTAG) cable program in a chain? Solution 1: The limiting factor on the number devices which can be in the JTAG chain is the drive capability of the TMS and TCK signals. Due to a 5KOhm pullup on the TMS pin, the maximum number of devices which the current JTAG cable is capable of driving is 7. In noisy environments that number can be less. If a larger chain of devices is needed additional buffering will be required. Please refer to the ISP Checklist at http://www.xilinx.com/xapp/xapp104.pdf End of Record #1272 - Last Modified: 12/17/99 13:31

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