I/O-Standards: HSTL vs. SSTL and others...

Hello all,

my question - I/O-Standards - I have searched the WWW up and down, but I'm really not happy what I have found. Especially HSTL vs. SSTL - what is better, newer... Some comments/hints/infos/pdfs from you?

Many thanks in advance Udo

Reply to
Udo
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Udo,

HSTL and SSTL are I/O standards, that is all.

Some chips use one, some use the other.

There is no such thing as "better" or "newer."

SSTL pre-dates HSTL (SSTL: Stub Series Terminated Logic) with a 3.3 V version, a 2.5V version, and a 1.8V version.

HSTL came right after SSTL(High-Speed Transceiver Logic) with a 1.5 volt version.

Many HSTL implementations were not fast enough, and a 1.8 volt version of HSTL was "created" in order to meet the speed that was desired (just ran the ASIC at 1.8 volts instead of 1.5 volts).

In the FPGA, the only difference between HSTL and SSTL is choice of drive strength, as the input comparator is identical in implementation for both (both use an externally provided reference voltage).

The termination schemes are the same (resistors to termination reference power supply).

There are four classes of termination, to handle single direction, or bi-directional data paths. Some classes may be better for your application than others.

The standards are often ignored when components are placed very close to the FPGA, and resistors are omitted (not used).

If you choose a standard, you are best to stick by it. If you decide to not follow the standard, you may be successful, but you are required to do all the signal integrity engineering to prove it works.

You are best to do the SI engineering (simulate the interfaces) anyway, as just because it is a standard does not mean you have used it properly.

Austin

Reply to
Austin Lesea

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