wcs@ho95e.ATT.COM (Bill.Stewart) (05/28/87)
While more RS232 applications use speeds up to 19200 bps, there are several products that talk 115kbps. Some are LAN-type products (EasyLAN), while others are for connecting laptops to machines with larger disk drives. How does this work? Is it RS-422? Can it work in a multi-drop application, or is it only point-to-point? It would be nice to connect a PC to a mini-computer at speeds like this; is there a way to make my 3B2 or VAXen connect to this? Thanks; -- # Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs
ward@chinet.UUCP (ward) (05/31/87)
> How does this work? > Is it RS-422? > Can it work multi-drop? > [can I] connect a PC to a mini-computer at speeds like this? The 115Kbps is done on the PC by Brooklyn Bridge, as another product, and I'm quite sure they do it by disabling interrupts. This severely limits the applications that can happen at either end while transfers are going on. For example, I've had the keyboard beep at me implying "stop typing" while doing the transfers (and I wasn't at the typeahead limit). No, its not RS-422. I run BB through about 50' of real Kludge wire (various ribbon cables, twisted 3-wire (pins 2,3,7), etc between two PC's, one upstairs, one down - BB works. I usually use it between my T1100+ and a PC.
davidsen@steinmetz.UUCP (06/01/87)
In article <1463@ho95e.ATT.COM> wcs@ho95e.ATT.COM (Bill.Stewart) writes: } While more RS232 applications use speeds up to 19200 bps, there are several } products that talk 115kbps. Some are LAN-type products (EasyLAN), while others } are for connecting laptops to machines with larger disk drives. } } How does this work? Is it RS-422? Can it work in a multi-drop application, or } is it only point-to-point? It would be nice to connect a PC to a mini-computer } at speeds like this; is there a way to make my 3B2 or VAXen connect to this? } Thanks; } -- } # Bill Stewart, AT&T Bell Labs 2G-202, Holmdel NJ 1-201-949-0705 ihnp4!ho95c!wcs The speed of the serial ports in the PC is set by putting a divisor into a latch. The output speed (baud rate) is then base/divisor. For the PC the base rate is 115200cps, which can be divided down to most common speeds. Most PCs and clones will go 19.2kb cleanly, with error rates increasing as you go 38.4kb and 76.8kb. This is often in the clock rates, rather than the line. At one point we ran a Cromemco system into a Honeywell mainframe at 76.8kb, running about 100 feet over a standard twisted pair. Error rate was essentially zero (routine 2-5MB files with zero errors). If you get into trouble, try using 2 stop bits (even 1.5 will often help. This allows a small amount of drift in the clock rate to be tolerated. Clock rate errors often slow up by allowing clean transmission in one direction, and error rate rising with packet length in the other. You can also play with synchronous connections, although you are unlikely to find many people who've done it. Kermit 2.29b should run the windowed protocol at at least 76.8kb, and give about 70% efficiency. -- bill davidsen (wedu@ge-crd.arpa) {chinet | philabs | sesimo}!steinmetz!crdos1!davidsen "Stupidity, like virtue, is its own reward" -me
hamilton@uxc.cso.uiuc.edu.UUCP (06/07/87)
davidsen@steinmetz (bill davidsen) says: > In article <1463@ho95e.ATT.COM> wcs@ho95e.ATT.COM (Bill.Stewart) writes: > } While more RS232 applications use speeds up to 19200 bps, there are several > } products that talk 115kbps. ... > } > } How does this work? Is it RS-422? ... > > The speed of the serial ports in the PC is set by putting a divisor > into a latch. The output speed (baud rate) is then base/divisor. For > the PC the base rate is 115200cps, which can be divided down to most > common speeds. Most PCs and clones will go 19.2kb cleanly, with error > rates increasing as you go 38.4kb and 76.8kb. ... > > Kermit 2.29b should run the windowed protocol at at least 76.8kb, and > give about 70% efficiency. i already knew about the divisor latch and the baud clock, so 19.2K, 38.4K, and even 115K bps are no surprize to me. 76.8K, tho! i'd really like to know how you do that on a stock pc serial port! how do you get the value 1.5 into the divisor latch?? :-) wayne hamilton U of Il and US Army Corps of Engineers CERL UUCP: {ihnp4,seismo,pur-ee,convex}!uiucuxc!hamilton ARPA: hamilton@uxc.cso.uiuc.edu USMail: Box 476, Urbana, IL 61801 CSNET: hamilton%uxc@uiuc.csnet Phone: (217)333-8703 CIS: [73047,544] PLink: w hamilton