Re: [uCsimm] Are the uCsimm I/O pins 5V Tolerant?

From: Sam Saprunoff (
Date: Thu Jan 27 2000 - 10:49:13 EST

Hi Tom,

Thanks for your reply! Yes, it is surprising that there is not a definitive answer within the specs... Further, I have also forwarded a message to the Motorola 683xx list to see if one of the FAEs will answer. If I find out a definitive answer from Motorola, I will post it to the list and to yourself.



Sam Saprunoff

  ----- Original Message -----
  From: Tom Walsh
  Sent: Wednesday, January 26, 2000 5:08 PM
  Subject: Re: [uCsimm] Are the uCsimm I/O pins 5V Tolerant?

  Sam Saprunoff wrote:
    Hello everyone,
    I was curious... Are the uCsimm I/O pins 5V Tolerant? I have been unable to
    verify this from searching through the uCsimm manual (Vdd -0.5 to +4.0,
    Vin -0.5 to +7.0), nor the Motorola MC68EZ328 users manual (Vdd/Vin -0.3 to

    Thanks in advance!

  No, they are not. You must use a logic family such as the 74LV which also provides for voltage level shifting. Nothing in the 68EZ328 User Manual says anything either way regarding the voltages on the i/o (and other) pins, as it usually happens, attaching a voltage higher than that of the the specified supply of A processor, generally results in damage to the pin through long term use.
  I would certainly welcome being wrong on this issue, but as yet, I have read no definitive documentation that specifically addresses the issue of TTL family interfacing. Rule of thumb? If they don't spec it, don't believe it!



Tom Walsh - WN3L - Embedded Systems Consultant - tom over_at mytoys(.)com
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"Windows? No thanks, I have work to do..."

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