GA I/O voltage?

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    As we all know, all VMs regardless of the language can impose huge run- time performance penalties, compared to native coding in native compiled languages. An STC-based Forth with optimal hand-coded assembler primitives can evade this cost to a large degree, so I won't be talking about that here. I'm thinking more of DTC, ITC and TTC-based forths. What I am interested in is: when is it better to sweat over the coding of forth words, squeezing every last ounce of speed out of them at the very likely cost of readability/maintainability, as opposed to just taking the time critical stuff and coding it as C and/or assembler primitives? Cheers Dave

GA I/O voltage?

Postby Mux » Thu, 18 Nov 2010 08:26:54 GMT

From what I've been able to gather, the I/O voltage is the same as the
core voltage on GA chips: 1.8v. Is this true or can you hook up a
separate ( say 3.3v ) supply for I/O?

Considering the dev-board will have RS232 connectors there either has
to be -or- there will be some additional level-shifting hardware on
the board.

-Mux

Re: GA I/O voltage?

Postby rickman » Fri, 19 Nov 2010 10:23:51 GMT



I don't really know any more than you do, but everything I have read
indicates the I/O Vdd is 1.8 volts just like the core.  The pin out of
the GA144 shows c+, i+ and a+ pins which I assume are core, I/O and
analog Vdd pins respectively.  The GA144 data sheet says Voh is 1.66
volts at Io = 10 mA and Vdd = 1.8 volts.  I don't see anything that
indicates other voltages are workable on the I/O Vdd pins.

As to the EIA-232 interface, you can use pretty much any TTL or low
voltage CMOS input as long as the EIA-232 levels are limited to not
damage the input.  But the output will require an actual driver chip
to be compatible with the spec as well as being sure to drive all
EIA-232 receivers.

Rick

Re: GA I/O voltage?

Postby Mux » Fri, 19 Nov 2010 12:50:50 GMT





That's how far I got :-) The devboard block-diagram shows a resister
between the RS232 and the chip but doesn't show anything going the
other way. Either way, it'd be nice to have some sort of level-
shifter, either on- or off-board.

Re: GA I/O voltage?

Postby Brad » Sun, 21 Nov 2010 00:00:48 GMT


The level shifters are built from a few transistors and resistors.
They steal power from the RS232 control pins.

-Brad

Re: GA I/O voltage?

Postby rickman » Sun, 21 Nov 2010 00:44:48 GMT





I'm curious, how do you know this?  Are you working with Green
Arrays?  Personally, I am a little disappointed that they are rigging
the 232 interface this way.  This puts more constraints on the
external 232 circuitry and is not of much point in an eval board
really.  If I were designing a toy or other product where every penny
counted I might do this, but otherwise it doesn't seem like a good
choice in an eval board.  Also, I've seen circuits like this that
don't work so well, but I assume that won't be the case here.

Rick

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1.GA I/O voltage?

From what I've been able to gather, the I/O voltage is the same as the
core voltage on GA chips: 1.8v. Is this true or can you hook up a
separate ( say 3.3v ) supply for I/O?

Considering the dev-board will have RS232 connectors there either has
to be -or- there will be some additional level-shifting hardware on
the board.

-Mux

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