Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
8 years ago

Max 10 JTAG Voltage Question

Hello,

I am designing a pcb around the 10M50SC (Max 10) 144 pin chip.

I am confused about what voltage the JTAG lines should have.

I've read that the pull up voltages for TMS and TDI should be 2.5V not 3.3V. It says so in the Pin Connection Guideline document.

"for configuration voltage of 2.5v, 3.0v or 3.3v, connect this pin through a 10kohm resistor to 2.5v to prevent voltage overshoot..."

But what voltage should Vcc have? I have given it 3.3V. Should it be 2.5V instead of 3.3 V? :confused:

I have given 3.3V to the VCCIO, VCCA..etc. on the Max 10 chip.

Isn't it kind of weird that the Max 10 is marketed as a chip which needs just one voltage... and now i need two separate voltages....

Thanks.

https://alteraforum.com/forum/attachment.php?attachmentid=13724&stc=1

3 Replies

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

    A single supply MAX10 device will be either supplied by 3.0 or 3.3V. It makes no sense to use a different supply than VCC_ONE for JTAG interface. Instead use effective clamp diodes if you worry about overshoot.

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

    --- Quote Start ---

    A single supply MAX10 device will be either supplied by 3.0 or 3.3V. It makes no sense to use a different supply than VCC_ONE for JTAG interface. Instead use effective clamp diodes if you worry about overshoot.

    --- Quote End ---

    Are you saying I should make the pull up voltage and Vcc voltage 3.3V on the JTAG?

    There would be harm done if it was 3.3V instead of 2.5V right?
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    8 years ago

    Back to the basics. The schematic in post# 1 makes no sense, the relevant point for possible JTAG overshoot is the USB cable supply voltage, not the pull-up resistor voltage. You have JTAG connector pin 4 connected to 3.3V, this might, if at all, be causing overshoot problems with long JTAG traces. The suggestion in the MAX 10 Design Guidelines is to power the USB cable with 2.5V, consequently the pull-up resistors will be connected to the same voltage.

    As previously stated, I won't provide an additional 2.5V supply in a single supply MAX 10 design (unless it's used for other purposes, e.g. LVDS IO). I prefer silicon or schottky clamp diodes for the JTAG port, e.g. one of the popular 6-pin ESD protection diode networks.