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Valued Contributor III
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why usb blaster need be set a max3378 (Level conversion chip)

i have seen the altera usb blaster ,there is nothing Level conversion IC ,but others always said that it should be a Level conversion ic in the usb blaster to fit the different Level of the target board... 

 

could you tell me why?
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Valued Contributor III
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Re: why usb blaster need be set a max3378 (Level conversion chip)

There's two different situations to consider; 

 

1) A USB-Blaster cable 

 

This type of USB-Blaster gets plugged into a target board via the 10-pin JTAG header. The VCC_TARGET pin on this header powers a dual-supply buffer inside the programmer so that the logic levels driven onto the JTAG pins are appropriate for the target board. 

 

2) On-board USB-Blaster 

 

When the USB-Blaster is included on a PCB, there is no need for a level translator, since the designer of the board will ensure that the USB-Blaster JTAG logic levels (typically from a MAX series CPLD) are appropriate for the JTAG device attached to it. 

 

If you were to use an on-board USB-Blaster schematic as the reference design for building a USB-Blaster cable, then you would need to *add* the level translator to your design. 

 

Cheers, 

Dave
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