Hello all, I just have three notes for those interested in the 683xx reset. 1. The manuals for this family (or at least the 68376 that I use) recommend a pullup resistor of 820 ohms. 2. Most reset chips or supervisors (that I found anyway) do not recommend this low of a resistance (820 ohms) for reset lines. They cannot handle the current draw. 3. On my board I use a MAX813L to drive an NPN BJT transistor, which then uses the 820 ohm pullup resistor for the reset. I made the mistake once of using a FET (instead of the BJT) and got burned because of the output capacitance of the FET (about 220 pF as I recall) and the fact that I use a 20 MHz clock oscillator IC to directly feed the chip (not the internal PLL). Hope this helps. Good luck. Jim -----Original Message----- From: Melear Charles-rdph40 [mailto:charles.melear@...] Sent: Thursday, June 19, 2003 9:41 AM To: '68300@yahoogroups.com' Subject: RE: [68300] Connecting to 332 Hello everyone, The reset pin of the 683xx family is not really made to be driven by a totem-pole type driver that is used by the Maxim part you mentioned. What you need to do is use an OPEN COLLECTOR Low Voltage Chip to drive the 68322's reset pin. You also need a 2 Kohm (or stronger) pull-up resistor on the RESET pin. IF YOU DO NOT HAVE A VERY STRONG PULL UP ON RESET YOUR CIRCUIT WILL NOT WORK!!!!!!!!!!!!!!!!! IF YOU DRIVE THE RESET PIN OF THE 68332 WITH A TOTEM POLE DRIVER (AS OPPOSED TO AN OPEN COLLECTOR DRIVER) YOUR CIRCUIT WILL BE MARGINAL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I have seen people use a totem pole driver (even Maximum's parts) and they use about a 5 Khom resistor (as I recall) between the output of the LVI chip and the 68332 RESET line. The whole problem that is being described here is that the LVI chip is NOT driving the RESET pin of the 68332 high fast enough. Remember, the RESET pin of the 68332 is an output when the 68332 is asserting reset. This makes the LVI chip FIGHT the 68332. Not a good thing. If you want to send me a copy of the schematic that just shows the reset circuitry, I'll take a look at it. Regards, Charlie -----Original Message----- From: Shyam mali [mailto:sscomputers2@...] Sent: Thursday, June 19, 2003 8:18 AM To: 68300@yahoogroups.com Subject: RE: [68300] Connecting to 332 The reset line of the 332 is tied to the MAX707 through a 4k7 series resistor. The design is proven, this board ain't. I tried second board of the same batch and it indicated the same problem. then i isolated all the pins (pulled up the reset and halt pin(which are shorted in my circuit) and observed the waveform... it was the same. Shyam -- --------- Original Message --------- DATE: Wed, 18 Jun 2003 18:15:41 From: Scott Newell <newell@...> To: 68300@yahoogroups.com Cc: >At 12:48 PM 6/18/2003 -0700, Melear Charles-rdph40 wrote: > >>Scott, >>I have seen the exact waveform you are describing. Here is how a >>Power ON Reset sequence works. > >Don't you mean Shyam Mali?--I'm not the original poster, I was replying to >the original poster. > >I'm betting on the missing reset line pullup too. > > >newell > > > ____________________________________________________________ Get advanced SPAM filtering on Webmail or POP Mail ... Get Lycos Mail! http://login.mail.lycos.com/r/referral?aid=27005 <http://login.mail.lycos.com/r/referral?aid=27005> < http://login.mail.lycos.com/r/referral?aid=27005 <http://login.mail.lycos.com/r/referral?aid=27005> > Yahoo! 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Message
RE: [68300] Connecting to 332
2003-06-19 by Godiska, Jim