[ Date Index ] [ Thread Index ] [ <= Previous by date / thread ] [ Next by date / thread => ]
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 03/06/12 13:00, Peter Lloyd-Jones wrote: > On 2 June 2012 22:11, Gordon Henderson <gordon+lug@xxxxxxxxxx> > wrote: > >> On Sat, 2 Jun 2012, Peter Lloyd-Jones wrote: >> >> Make something idiot proof and you'll just find a better class >> of idiot ;-) >> >> I resemble that remark! > > Not only that I am showing my age. Having looked at the GPIO I > thought "this is a job for a 8255", this would give one 24 lines > and are (were) very cheap, however I do not think they make them > any longer :( The 82C55A, which is a version of this is still available. (496-763 from RS.) Also any PC with a parallel port is likely to have something capable of emulating an 8255. > However I have stumbled across an old circuit using 74LS151,138s > 74154s and 7404 which should give 128 ins and 128 outs! (It was > for the BBC user port which had 10 lines.) Note that the Pi's GPIO ports run at 3.3V. So you'd either want to use 74HC to interface to it or incorporate some form of level shifter. Since the Pi will give you up to 17 you could do use something more like one 74HC154; sixteen 74HC244s for the input side and sixteen 74HC373s for the output side. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk/Low8ACgkQsoRLMhsZpFeVmQCfTl1AroI26j92deuTjPrrrUWs iekAn1kufc2JVPG4xUjtatvwsdvA4i4N =1qwI -----END PGP SIGNATURE----- -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/listfaq