Programmable Devices
CPLDs, FPGAs, SoC FPGAs, Configuration, and Transceivers
Announcements
The Intel sign-in experience is changing in February to support enhanced security controls. If you sign in, click here for more information.
19680 Discussions

Cyclone IV JTAG pins connected to VCCA (2.5V) with IO bank of 3.3V

HAlex
Beginner
159 Views

Hello

 

I am using Cyclone IV GX (EP4CGX150CF23C8N).

JTAG and configuration device (AS - EPCQ128ASI16N) connection done as described on figure 8-29 (page 220 of Cyclone IV device handbook Volume 1).

All VCCIO in my project are 3.3V.

I am wondering is it correct to connect TMS, TDI (with pull-up resistors) and JTAG connector pin 4 (for USB/BYTE blaster) to VCCA (2.5V) while VCCIO = 3.3V?

In page 210 of handbook it is also mentioned:

"All the JTAG input pins are powered by the VCCIO pin and support the LVTTL I/O
standard only."

 

Thank you

0 Kudos
1 Solution
ak6dn
Valued Contributor III
139 Views

For 3.3V LVTTL, the spec for VIH(min) is 1.7V and VIH(max) is 3.6V.  So a pullup to a voltage between these limits (2.5V) is OK.

Normally tho one would connect the pullup to the same voltage source as drives the VCCIO for those I/O pins.

The only concern would be what are the powerup characteristics of the 2.5V and 3.3V rails in your system?

Do they powerup simultaneously, or is there a significant time differential in their ramp rates?

For example, if the 2.5V rail turns on significantly later, you could get into the situation where the pullup to 2.5V is actually a pulldown.

Personally I would connect the pullups to the same voltage source that drives the VCCIO pin for those I/Os.

View solution in original post

2 Replies
ak6dn
Valued Contributor III
140 Views

For 3.3V LVTTL, the spec for VIH(min) is 1.7V and VIH(max) is 3.6V.  So a pullup to a voltage between these limits (2.5V) is OK.

Normally tho one would connect the pullup to the same voltage source as drives the VCCIO for those I/O pins.

The only concern would be what are the powerup characteristics of the 2.5V and 3.3V rails in your system?

Do they powerup simultaneously, or is there a significant time differential in their ramp rates?

For example, if the 2.5V rail turns on significantly later, you could get into the situation where the pullup to 2.5V is actually a pulldown.

Personally I would connect the pullups to the same voltage source that drives the VCCIO pin for those I/Os.

HAlex
Beginner
121 Views

Hello

 

My 2.5V turns ON after 3.3V (DC-DC regulation from 3.3V to 2.5V) with S.S setup of few mSec (less than 5mSec).

Standard POR time in Cyclone is up to 50mSec - so it should be ok.

But just to be on the safe side I decided to do also an alternative connection for VCCIO (of 3.3V - Bank 9).

HAlex_0-1652082020302.png

By default I will assembly resistors only to VCCA (2.5V).

Thank you very much

 

Alex

Reply