selmar@small-u.UUCP ( elmar folba) (02/11/88)
Hi everybody, I need to connect two systems, both equipped with IEEE488 interface but a few hundred feet distant from each others. I'm told there exist totally passive and transparent extender gadgets which bridge the distance using a fibre optic cable. Has anybody had practical experience with such devices? Thank you for any hints. Kind regards, Elmar Folba C.H.F.Mueller GmbH Am Stadtrand 39 D-2000 Hamburg 70, West Germany Phone (+49 40) 69425 168 USENET mail: ...!unido!small-u!selmar
rjn@hpfcmp.HP.COM (Bob Niland) (02/18/88)
re: fibre optic IEEE-488 extension HP's current product in this line is the 37204A. It uses coaxial cable in the standard configuration, and duplex fibre as an option. Two units may be separated by up to 1250m (multiple stations are also possible for further extension). I am presently using a pair of earlier 37203As (slower) on coax cable. The boxes transparently pass all IEEE-488 (HP-IB) traffic, although there is a consideration concerning parallel poll (PPOLL). The only other limitation that might affect you is speed. The HP37204As pass traffic at a max rate of 60 Kbytes/sec. They have been satisfactory in my use with a high-speed laser printer. I have also tested them with an HP-IB disc, where a customer had to locate an expensive removable drive outside the hostile enviroment that contained the computer. It worked, with some performance degradation (the disc had a 1 Mbyte/sec transfer rate). The 60K rate might be an issue if the device at either end is synchronous - i.e. must send or accept data at a fixed rate higher than 60K, and will lose it if the link is any slower. The only HP device I am aware of that might behave this way is the 7970E/7971A tape drive. Regarding PPOLL: PPOLL is the only '488 operation that is not governed by handshake. PPOLL is timed (Assert ATN+EOI, wait for one or more DIO lines to go true). The IEEE spec says to wait at least 2 uSec for PPOLL response. This is far too brief for the propagation delay of any likely extension. Your computer may implement this sense delay in either software or hardware. You may have trouble discovering the value selected for you, and if too short, you may be unable to change it. On the other hand, you may have no need to perform PPOLLs, in which case this is not a concern. HP UN*X systems employ a 100 uSec PPOLL sense delay to permit use of extenders with polled HP-IB computer peripherals. This is adequate for distances up to the full 1250m using a single pair of 37204As. Bob Niland ARPA:rjn%hpfcrjn@hplabs.HP.COM UUCP:[ihnp4|hplabs]!hpfcla!rjn