Path: utzoo!utgpu!watmath!isishq!f171.n221.z1.FIDONET.ORG!izot From: izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh) Newsgroups: comp.sys.cbm Subject: Rs-232 standard? Message-ID: <1445.23E5B7E7@isishq.FIDONET.ORG> Date: 28 Jan 89 04:48:33 GMT Sender: ufgate@isishq.FIDONET.ORG (newsout1.25) Organization: FidoNet node 1:221/171 - Izot's Swamp, Kitchener ON Lines: 63 > From: aliu@sal57.usc.edu (Alejandro Liu) > Message-ID: <2471@nunki.usc.edu> > > How does the Rs-232 standard is implemented in the Commodore? Fred (Bowen) covered that well enough. > What is the Rs-232 standard? Formally known as the EIA (Electronics Industry of America) Recommended Standard (RS) number 232C, it specifies a 25-pin "D"-shaped connector and gives approximate meaning to most of its lines, and specifies signal voltages to be used on those lines. In the real world, connecting two devices via an RS-232C cable depends on how each device implements the approximate meaning implied by the names give to the lines. As Fred said, one can usually get away with three lines: transmit data, receive data, and ground (needed for electrical reference, but useful for shielding). However, modems (especially the high-speed variety) and printers need the other lines to provide control and information. > Also, I while searching for information about the Commodore > implementation of the Rs232, I came across a comment saying that > Commodore wanted to keep the Configuration register compatible with > the UART chip. What is this UART? UART = Universal Asynchronous Receiver/Transmitter. Actually, Joe Greco is correct in pointing out that the ROMs emulate the 6551 ACIA (Asynchronous Comminucations Interface Adapter - technically it's not a UART because it is NOT "universal", principally because it can work only at specific speeds while true UARTs can be set to any speed by a divider register). The 6551 emulation is close but not exact, and the code generates correct timing only at speeds under 800 bits per second (C64). Although a kludge documented by Steve Punter (I posted the article in this newsgroup a few weeks back, I think) allows passable 1200 bps and precarious 2400 bps, higher speeds and reliability require carefully written and optimized software drivers. I'm actually very saddened that Commodore decided not to include a real 6551 in the C64. Although the designers had no way of knowing how many C64s would end up connected to modems, the C64 was at the forefront of bringing modems into the home, and having a 6551 and less demanding serial disk timing would have done much to enhance the C64's position as "the communicating home computer". =========================================================================== Internet: Geoffrey.Welsh@f171.n221.z1.fidonet.org | 66 Mooregate Crescent Usenet: watmath!isishq!izot | Suite 602 FidoNet: Geoffrey Welsh on 1:221/171 | Kitchener, Ontario PunterNet: 7/Geoffrey Welsh | N2M 5E6 CANADA BBS: (519) 742-8939 24h 7d 300/1200/2400bps | (519) 741-9553 =========================================================================== | "I don't need a disclaimer. No one pays any attention to what I say." | =========================================================================== -- Geoffrey Welsh - via FidoNet node 1:221/162 UUCP: ...!watmath!isishq!171!izot Internet: izot@f171.n221.z1.FIDONET.ORG