74ls593 high VoL ?

[bitman]

Can someone help me understand if what I'm observing is lining up with the data sheet?  I have a few 74LS593s and while it works great, the output voltage I'm seeing when the chip is "disabling output" (CCKEN high), G and !G are both LOW I see about 1.5->1.7 volts on the outputs (Q lines). If I read the datasheet right I should only be expecting around 0.4volts?  I realize this isn't tri-state so I'm probably asking for problems as I connected it straight to the bus which is causing issues (other chips that aren't tri-state seems to do the same).

So I'm confused in regards to "facts vs. datasheet" here: http://pdf1.alldatasheet.com/datasheet-pdf/view/28020/TI/SN74LS593N.html
Just to be sure I took a picture of the chip just in case I've got the wrong data sheet.

[Ian.M]

Page 2 top left shows that the I/O lines in input mode look like a 25K pullup to Vdd clamped at about 1.5V with a Schottky diode so they can only source current.   If you want a true tristate, use CMOS logic not the bipolar TTL families, but beware of input threshold differences degrading noise margins in a mixed system and cross-family fanout limits.

[bitman]

Page 2 top left shows that the I/O lines in input mode look like a 25K pullup to Vdd clamped at about 1.5V with a Schottky diode so they can only source current.   If you want a true tristate, use CMOS logic not the bipolar TTL families, but beware of input threshold differences degrading noise margins in a mixed system and cross-family fanout limits.

The title I found claims tri-state, and "typical of Q outputs" looks very much like a traditional tri-state setup?  Anyway, I'm still struggling with why the sheet later states 0.4 volt - but I guess that's when there's an active low signal on the line. In this case there's no active signal.

I guess I need to figure out a better mechanism connecting this counter (PC) to a bus. Thanks for very fast feedback!

[Ian.M]

It should be noted that an bipolar TTL output only tristate buffer wouldn't have the same issue.  Its only bidirectional ones that have the input circuit acting as a weak pullup to an intermediate voltage.

[bitman]

So I changed my pulldown resistor on the "bus" from 1K to 470 - and now the lines all dropped to way below 1v (approx 400mv). That fixes my problem, but now I need to figure out WHY that fixed it. It's fun learning - but at times it's frustrating too.
Thanks again @Ian.M for a quick response.