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Altera_Forum's avatar
Altera_Forum
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13 years ago

Cyclone IV E JTAG inputs board pull-up to VCCA instead of VCCIO?

Shouldn't Cyclone IV E JTAG inputs be pulled up on the board to VCCIO (3.3V in our case) instead of VCCA (2.5V) as recommended in the pin connections guidelines? The device handbook says "all the JTAG input pins are powered by the VCCIO pin and support the LVTTL I/O standard only". If you were to pullup to only VCCA wouldn't there be CMOS delta ICC current since the input is not all the way to the rail? The handbook also states "The LVTTL/LVCMOS I/O standard input pins can only meet the VIH and VIL levels according to bank voltage level". By tying off these inputs to 2.5V instead of 3.3V doesn't his reduce your noise margin since you are sitting closer to VIH?

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    Hi,

    I've implemented the guideline to pull TMS and TDI to VCCA (as shown in 8-23 and required for 2.5, 3.0 and 3.3V I/O) which is a well working combination.

    Your question on I/O levels is answered in "Configuration and JTAG Pin I/O Requirements" (p.8-5): "Cyclone IV devices are manufactured usingt the TSMC 60nm low-k dielectric process. Although Cyclone IV devices use TSMC 2.5-V transistor technology in the I/O buffers, the devices are compatible and able to interface with 2.5, 3.0 and 3.3-V configuration voltage standards..."

    (For JTAG the VCCA is to be connected to the Header and is used by the USB-Blaster as I/O supply...)