Re: Missing Schmitt Gates??

On Wed, 05 Dec 2007 10:01:27 -0500, Spehro Pefhany
<speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Wed, 05 Dec 2007 08:44:43 -0600, John Fields
<jfields@xxxxxxxxxxxxxxxxxxxxx> wrote:

I found no mention of self-oscillation, and with that tightly
defined trigger point and no hysteresis, it doesn't seem likely
that's a Schmitt trigger.

No, it's not clear just from the data ***, however IDRC (I Did
Recall Correctly-- hey, it happens..), if you look further back in
your book to AP-155, _Oscillators for Microcontrollers_ (at least I
think it's bound into that edition) and you'll find the following:-

----
MCS-48 Oscillator

The NMOS and HMOS MCS-48 oscillator is shown in
Figure 21. It differs from the 8051 in that its inverting
amplifier is a Schmitt Trigger. This configuration was
chosen to prevent crosstalk from the TO pin, which is
adjacent to the XTAL1 pin.
...
----
(they go on to discuss the thoroughly nasty "relaxation mode" at
~50kHz and the possible associated problems transitioning to proper
crystal operation, with some nice oscilloscope photos)

http://download.intel.com/design/mcs51/applnots/23065901.pdf

(see PDF pages 20-24).

Although the MCS48 NMOS chip is LONG past obsolete, this is still a
good application note and I recommend it to anyone working with micros
and using the internal oscillator.

---
Indeed. Thanks :-)


--
JF
.