troy@fornax.UUCP (Troy Brooks) (05/15/91)
Thanks to everyone for their helpful postings and mail. Here is a brief summary: - I'm trying to hook up the RS-232 serial port on our SGI Personal Iris workstation to a MIDI interface; the problem is, the baud rates are different, and MIDI requires optoisolation. It is possible to set the baud rate of the port in software, but the only available speeds are 300, 600, 1200, 2400, 4800, 9600, 19200, 38400 baud. (Also 110 or something really small; I forget.) Since the MIDI spec is 31.25 kbaud, (+/- 1%), none of these will work. Since I don't want to rip open the Iris and perform radical surgery, I needed an interface with an external UART. The interfaces for the Mac and the NeXT are for the RS-422 serial port, which allows you to set the baud rate externally. The interfaces for IBM type machines either use a card to get a fast enough baud rate (like the MPU-401 from Roland), or they have a bizarre-o baud rate of 28.8 kbaud. (Why? I don't know; just to be different.) There are two companies that make what I need, apparently. (There may be more, but I only heard about these two.) One is Key Electronics, in Fort Worth, Texas, which makes the MS-114 for U$229, plus $20 for the power supply. It works at 19.2 kbaud or 38.4 kbaud, and has 4 bytes of buffering. (Yes, 4, count 'em 4) So, according to them, unless you really need heavy throughput, go with 19.2 kbaud, because the 38.4 kbaud version uses some handshaking stuff with the external UART, and is not always happy. The other unit is made in Somerset, England, by Hinton Instruments, and is apparently really good, but really expensive, too. (~$600) I plan on buying the Key Electronics one; I heard from people using it with Sun machines, and I don't need heavy throughput, so it seems best. If anyone is interested, e-mail me (troy@cs.sfu.ca) and I'll let you know how it works out. Thanks again to everyone who responded; you saved me a lot of work and wasted effort! Troy