... send to the piclist this time? ... "used a 74LS04" Substitute the 'LS04' with a 74HC14 and you've got my solution. The HC14 will (Schmitt Trigger) assure 'clean', sharp tiggering on slow rise/fall time serial input signals ... Also, I'm not too sure a *true* "LS04" gate can actually pulled low through a 330K Ohm resistor - a true TTL LS (bipolar, Low-power Schottky) gate is spec'd at more like .4 mA low-level input current. This would require a voltage of -132 VDC to be applied to the 330K Ohm resistor to supply .4 mA of current for a logic low input to the gate! With a CMOS gate - this is not an issue. Just make sure the device family includes built-in "clamping" diodes (normally associated/used with/for static-protection) ... Jim ----- Original Message ----- From: "Dale Botkin" To: Sent: Saturday, September 08, 2001 9:39 AM Subject: Re: [PIC]:Simple RS232 hardware > > I'm sure this must have been covered before but a search of piclist.com > > failed to find anything... Anyway what would you recommend as the > > simplest/minimal hardware RS232 interface for use between a PIC and a modern > > PC? This is *not* for a production product I would just like to be able to > > include a very cheap interface on a home project for occasional > > diagnostic/config use. Can I get away without using a MAX* converter? What > > are the pros/cons? What would be your suggested circuit? > > For one-off, home projects, I'm in the "resistor-to-PIC" crowd. I've used it a dozen or so times with no problems... but of course people are right, it's not true EIA-232, it's not guaranteed to work, etc etc. Truth is it will work in the vast majority of cases, but I'd probably not use it in a production device. I have seen it done in commercial products though, often. Mice come to mind. > > Pros: Dirt cheap. Extremely simple. Dirt cheap. > Cons: You HAVE to do bit-banged comms, since there is no way to invert UART data. Also not precisely to PIC datasheet specs. Of course, neither is at least one of Microchip's app notes using 110VAC directly to a PIC pin via a high-value resistor. I figure if they do it so can I at less than 10% of the voltage. > > In those cases where I had to use the hardware UART and didn't have a MAX232 type device handy, I have (in a pinch, temporarily) used a 74LS04 in place of a MAX232. Just use two inverter sections to invert the TxD and RxD; I used 330K Ohm resistors between the LS04 and the PC. I wouldn't say I recommend this, but it has worked for me -- like I said, in a pinch and as a temporary thing. > > Dale > -- > A train stops at a train station. A bus stops at a bus station. > On my desk I have a workstation... > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu