[Coco] 8-Bit Microcomputers

[Theodore Evans (Alex)]

On Jan 25, 2004, at 6:14 PM, David Hazelton wrote:

> KnudsenMJ at aol.com wrote:
>
>> industry-standard floppy interface was a real gift, and we didn't 
>> waste it!
>> Also, despite the jokes about Tandy's serial printers and modems, 
>> that interface was standard RS-232, once you got past the 4-pin DIN 
>> connector (which hung from the walls in Rad Shack store).  And the 
>> manual documented the pinouts.
>
> Actually, it wasn't standard RS-232, Since if I remember right it was 
> +3/-3v instead of +5/-5v.  This actually helped me at a job I once 
> had.  I worked at Cabletron and I had a sales person call me to ask 
> why Cabletron's Terminal Server (Xylogic's Annex3 in a Cabletron hub) 
> couldn't see a RS-232 device.  A Unix machine was polling the ports to 
> read power gauges.  While Cabletron's Terminal Server sat there 
> blankly along with 2 other companies Terminal Servers, Cisco's 
> Terminal Server was reading the gauges happily.  It made Cabletron 
> look bad.  Well, Cabletron at the time resold Cisco routers redesigned 
> for thier hub, so I called up a Cisco engineer to ask him, he didn't 
> know off the top of his head, but when I mentioned that it acted like 
> the guage voltage wasn't high enough and that I had seen a system that 
> RS-232 was based as +3/-3v, he looked at the schematics.  True enough 
> that was the problem, testing the gauges voltage, it never went above 
> 3.5 volts.  Cabletron lost the contract and Cisco won.

In either case it wouldn't be standard RS-232.  Early RS-232 was 
+12/-12.  Later the standard was expanded to take -12-0/+5-+12 for 
signaling (about the same time that RS-422 came out).  Long before the 
expanded signaling became standard nearly all equipment would accept 
the expanded signaling levels.