Path: ...!2.eu.feeder.erje.net!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: port pins Date: Thu, 12 Sep 2024 20:08:33 -0000 (UTC) Organization: A noiseless patient Spider Lines: 42 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 12 Sep 2024 22:08:33 +0200 (CEST) Injection-Info: dont-email.me; posting-host="4eb4ff453a46b8df165ba0e54238d09f"; logging-data="444083"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/LHxfzd9wpiEM+OuEDh2GM" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:BQdAmDXLGUAjWJ2MF2T/sFy6+t0= sha1:gyVJ7hvMPdl0lyVqT2LJ2xSCKj0= Bytes: 2581 piglet wrote: > john larkin wrote: >> Something I've wondered about: >> >> Suppose we have a c program running on some little uP, and it has some >> integer variable value, 8 or 12 bits or something, and wants to drive >> a parallel DAC off-chip. >> >> The msb...lsb bits of the variable obviously have to get to the right >> pins of the DAC. >> >> So, in general, how does one pick the physical i/o port pins on the >> uP, to get the order right? The PCB layout is easiest if we just wire >> the DAC to the handiest port pins. >> >> One could test and bit-bang each bit and port individually, and then >> strobe the DAC, but that's inelegant. >> >> In the RP2040 chip, one can apparently write to a register in a >> PIO/state machine block, where each bit of the register can be >> assigned to drive a physical port pin. I think there are some >> constraints on the selected pins. >> >> >> > > I didn’t know that now exists - but sounds super useful. Would have saved > much headache if it had been around years ago. > We sometimes use the LPC804, which has a gigantic pin mux—you can effectively put any function on any pin. IIRC reset and isp are a bit special, but all the gpio and built-in peripheral functions can be configured any way you like. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics