Buffers/Line drivers for 6pin JTAG?
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Buffers/Line drivers for 6pin JTAG?

 
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Telenochek
Guest
Posted: Wed Dec 21, 2005 11:54 pm    Post subject: Buffers/Line drivers for 6pin JTAG? Reply with quote
Hello, everyone!
I am trying to adapt Spartan 3 Starter Kit board as a standalone board
for one of my projects.
To download configuration to FPGA I want to use 6 pin serial JTAG.
My question is: are there any strict specifications for the line
driver that drives TDO line back to the PC? Any links addressing this
issue would be very welcome!

TMS, TCK, TDI lines are driven by drivers inside the Xilinx parallel
cable (which take the power from PC parallel port). They are Schmitt
trigger type and quite fast: NL37WZ17
I was wondering if the TDO line buffer/driver needs to adhere to
similar specifications?
The board is to operate @ 3V.

Thank you!
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John Adair
Guest
Posted: Thu Dec 22, 2005 12:52 am    Post subject: Re: Buffers/Line drivers for 6pin JTAG? Reply with quote
I don't have the Starter Kit schematic to hand so this is a general
statement. If the Spartan-3 is the last device in the chain then you should
have sharpish edges on TDO as Spartan-3 has an active totem-pole o/p for
TDO. This is not always the case as some Xilinx devices have an open drain
drive and rely on a pullup for the high level. In the later edges can be
slowish so schmitt is possibly better. That said Parallel Cable III uses
74xx125 drivers which are not schmitt.

John Adair
Enterpoint Ltd. - Home of Raggedstone1. The $90 Spartan-3 Development Board.
http://www.enterpoint.co.uk


"Telenochek" <interpasha@hotmail.com> wrote in message
news:1135187684.760646.76040@o13g2000cwo.googlegroups.com...
Quote:
Hello, everyone!
I am trying to adapt Spartan 3 Starter Kit board as a standalone board
for one of my projects.
To download configuration to FPGA I want to use 6 pin serial JTAG.
My question is: are there any strict specifications for the line
driver that drives TDO line back to the PC? Any links addressing this
issue would be very welcome!

TMS, TCK, TDI lines are driven by drivers inside the Xilinx parallel
cable (which take the power from PC parallel port). They are Schmitt
trigger type and quite fast: NL37WZ17
I was wondering if the TDO line buffer/driver needs to adhere to
similar specifications?
The board is to operate @ 3V.

Thank you!
Back to top
Telenochek
Guest
Posted: Thu Dec 22, 2005 1:15 am    Post subject: Re: Buffers/Line drivers for 6pin JTAG? Reply with quote
Thanks for your help!
I think a 74LX1G126 will work with +/- 24mA sink & 10ns/V rise/fall
time.
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