Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!unsvax!uns-helios!alfter From: alfter@uns-helios.nevada.edu (SCOTT ALFTER) Newsgroups: comp.sys.apple2 Subject: hardware handshaking through a modem Message-ID: <2092@unsvax.NEVADA.EDU> Date: 6 Oct 90 04:45:07 GMT Sender: news@unsvax.NEVADA.EDU Reply-To: alfter@uns-helios.nevada.edu (SCOTT ALFTER) Organization: Univ of Nevada System Computing Services - Las Vegas Lines: 32 I'm working on a telecomm system for the Apple II; presently I'm making a modem driver for a Hayes Smartmodem hooked through an Apple Super Serial Card. (My actual setup is an Applied Engineering DataLink 2400, but what's the difference to the driver? :-) ) This is an interrupt-driven driver. The interrupt "daemon" dumps incoming text into a 256-byte buffer, where it can be pulled out by the telecomm program's routines when they need it. A feature I recently added was XON/XOFF handshaking. When the buffer contains 128 characters, the daemon automatically sends XOFF. XON is sent to resume operation when the buffer's contents drop to 64 characters. XON/XOFF handshaking is fine for an interactive session, but what about file transfers? You need all 256 possible byte values available for most file transfer protocols (some, such as Kermit, make do with less), so you can't use handshaking that adds stuff to the bitstream. The obvious solution is hardware handshaking--playing with the DTR line. However, this doesn't seem to work. I reassembled my modem driver for DTR instead of XON/XOFF and called a BBS at 2400 baud, using a BASIC program to interface with the ML routines. With XON/ XOFF, incoming text was whole--it appeared slowly, but you'd get it all. With DTR, though, large chunks of text would be missing. All I'm doing is playing with bit 0 of the ACIA's command register--a 1 means ready, 0 should tell the remote device not to send. My Imagewriter works this way; are modems different? Do handshaking signals get sent, or is XON/XOFF the only possibility? Thanx in advance for any help with this problem. ------------------------------------------------------------------------------- Scott Alfter _/_ / v \ Apple II: Internet: alfter@uns-helios.nevada.edu ( ( the power to be your best! GEnie: S.ALFTER \_^_/