Post by thread:[PIC]: Bus Resistors.

Hey all, Bit of a stupid question, but I was just wondering if I should add a resistor between each pin of the pic (18F8520) and memory (Am29LV800B) on Bus AD[0-15] (link at end of paragraph). I figure it should be fine without since the pic shouldn't let me put both devices in output state. http://muss.cis.mcmaster.ca/~tufgaraj/membus.jpg What is standard practice with memory if you control both the tristates of the MCU amd memory, do you add a resistor to each data line to prevent the possibility of shorting VCC to gnd, if both happend to be outputs at the same time and one is high and the other is low? Thanks in Advance, Aaron -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> I figure it should be fine without since the pic shouldn't let me > put both devices in output state In microprocessor mode series buss resistors aren't necessary because you have control of /OE. In microcontroller mode they aren't necessary because you *should* have control of /OE. You could put a pullup on it though in case RJ1 floats for some reason -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Thanks for the response Jinx. I'm going to use Extended Microcontroller mode. Anyone ever experience any gotchas with the Extrenal memory mode? It's my first time using the external memory bus on the 18F8720, and there's too many connections to justify prototyping it, so I want to make sure it's done right, since I'm going right to 4-layer PCB. Thanks in advance, Aaron > In microprocessor mode series buss resistors aren't necessary because > you have control of /OE. In microcontroller mode they aren't > necessary because you *should* have control of /OE. You could put a > pullup on it though in case RJ1 floats for some reason -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Tue, Jul 06, 2004 at 03:32:37PM -0400, A.J. Tufgar wrote: > Thanks for the response Jinx. I'm going to use Extended > Microcontroller mode. Anyone ever experience any gotchas with the > Extrenal memory mode? It's my first time using the external memory > bus on the 18F8720, and there's too many connections to justify > prototyping it, so I want to make sure it's done right, since I'm > going right to 4-layer PCB. You could always put pads/holes in anyway, and if it turns out you don't need them, then put a 0-Ohm resistor or link in. (Not done any boards myself so far, just seen others do this.) Chris -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics