I bought the 74189 TTL RAM chip and hooked it up but I can't seem to get it function.


simulate this circuit – Schematic created using CircuitLab

I hooked it all up and set the D1 to HIGH. Then I hold CE down, press WE then let go of CE. If I did this according to the datasheet then pressing CE should cause the LEDs to to show what I stored. They don't. (Yes I know the LEDs are inverted but the chips sense outputs are inverted too)

Here's the datasheet and the store page: http://www.jameco.com/Jameco/Products/ProdDS/49883.pdf -- Datasheet http://bit.ly/1oZL7hy -- Store Page

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    \$\begingroup\$ Where are the pullup resistors for your switches? \$\endgroup\$
    – Dave Tweed
    Commented Mar 6, 2016 at 14:13
  • \$\begingroup\$ I thought pullup resistors were only necessary for CMOS. \$\endgroup\$ Commented Mar 6, 2016 at 14:22
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    \$\begingroup\$ Look at the datasheet again. Specifically, \$I_{IH}\$ on page 7. Note that the value given is positive (40 uA), which means that the external circuit must source current in order to drive the input high -- i.e., above 2.4 V. You need pullup resistors. A value like 10K on each switch should work well. \$\endgroup\$
    – Dave Tweed
    Commented Mar 6, 2016 at 14:41
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    \$\begingroup\$ Note that this is a very old chip. They were only made in the 1970s. The only databook I have that has anything on it dates from 1976, and by 1981, it was no longer listed in any of them. Depending on how it was stored over the past 40 years, the chip you have may simply have expired from old age. \$\endgroup\$
    – Dave Tweed
    Commented Mar 6, 2016 at 14:51
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    \$\begingroup\$ @supercat - I struggled with this problem a while back. At first glance all of the 74xxx RAM and PROM chips were apparently made obsolete long before they actually were obsolete. What actually happened is that they were renamed. Or rather, were never consistently named in the first place, and eventually everyone stopped using the 74xxx designations. 74LS89 became a 3101A (due to many manufacturers copying Intel's naming scheme), or an 82S25, while a 74LS189 became a 27S03 (and the much more sensible 74LS219 , which was the same except it didn't have inverting outputs) became a 27S05. \$\endgroup\$
    – Jules
    Commented Jul 10, 2018 at 18:34

1 Answer 1


The issue was the equipment I was using. The wires I had bought were faulty.


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