Newsgroups: comp.sys.apple2.comm Path: blue.weeg.uiowa.edu!news.uiowa.edu!uunet!MathWorks.Com!europa.eng.gtefsd.com!howland.reston.ans.net!wupost!waikato!comp.vuw.ac.nz!actrix.gen.nz!dempson From: dempson@actrix.gen.nz (David Empson) Subject: Re: PIN-OUT for Apple //c modem port Message-ID: Organization: Actrix Information Exchange References: Date: Wed, 12 Oct 1994 13:09:24 GMT Lines: 59 In article , Matthew B. Wood wrote: > > What is the DIN-5 pinout from the //c modem port? Anyone know? I > tried searching ftp.apple.com but the tech files didn't seem to have > it. And do they still make //c modem port -to- db-25 cables? Please > post some info if you can help. Thanx in advance! I've answered this question so many times I no longer need to look it up in a manual. If this isn't in the comp.sys.apple2 FAQ, I want to know why not! The modem and printer ports are identical as far as hardware is concerned. Looking at the back of the IIc, the pins are numbered as follows: 5 1 4 2 3 The functions are: 1 DTR (flow control out of IIc) 2 TxD (data out of IIc) 3 Ground 4 RxD (data in to IIc) 5 DSR (flow control in to IIc) The names "DTR" and "DSR" are not particularly accurate, but they reflect the usual functions of the pins. They actually go to the RTS and DCD control lines on the 6551 ACIA. Deactivating RTS ("DTR") will prevent the IIc from transmitting. If the external device deactivates DCD ("DSR"), the IIc will stop receiving. These side effects cause problems when the IIc is used with "hardware handshaking". The effect is that if the IIc tells the modem to stop transmitting (via RTS), the IIc will also stop transmitting. If the modem tells the IIc to stop transmitting (via DCD), any data subsequently sent by the modem will not be received by the IIc. If you have the original IIc motherboard, you might have problems operating the serial port with some devices. Due to a design shortcut, the original IIc motherboard transmits and receives about 3% too slow, which can cause problems with smart modems in particular. (My ZyXEL U-1496E+ doesn't seem to mind, and neither does any computer I've connected the IIc to.) If you can demonstrate this problem to an Apple dealer, you should be able to get a free motherboard replacement. There is an authorization code that the dealer needs (ODL660, I think) so that Apple will reimburse them for the upgrade. -- David Empson dempson@actrix.gen.nz Snail mail: P.O. Box 27-103, Wellington, New Zealand