SUMMARY: scsiTerminal server

From: John DiMarco (
Date: Wed Dec 02 1992 - 17:50:50 CST

As promised, here is a summary of the responses I received to my request
for information and experiences with the Central Data scsiTerminal server (STS).

I only received a few responses, but they were generally quite positive.
People seemed quite pleased with its throughput, and the fact that it provides
full hardware flow control in both directions.

Those that mentioned it seemed happy with Central Data's support.

One persion mentioned that Central Data's drivers did not support Solbourne or
Sun 4/490 (VME) SCSI interfaces.

Surprisingly, nobody provided any data about how the STS coexists with disks
and other SCSI devices on the SCSI bus. This isn't an issue with us (we
happen to have an unused SCSI interface on the machine we're planning to
add it to), but might be an issue for others.

We're probably going to go ahead and order one.

Many thanks to: (Tom Rushworth )
Pete Hartman <> (C. R. Oldham) (Mike Andrews)



John DiMarco                                    
Computing Disciplines Facility Systems Manager  
University of Toronto                                     EA201B,(416)978-1928

------------- ORIGINAL post:

>Does anyone have any experiences with or opinions about Central Data's >"scsiTerminal Server", esp. connected to a sun? If so, I'd be interested in >hearing them. For instance, how does it behave under load? What is its >impact on the host? The scsi bus? > >Please respond via e-mail; I'll post a summary to this newsgroup. > >For the unfamiliar, the "scsiTerminal Server" is a device which allows >one to add serial (and sometimes parallel) ports to a machine via the scsi >interface. > >Thanks, > >John

------------- SUMMARY:


[ Mark works for Central Data, and sent me this data sheet. -jdd ]

scsiTerminal Server 16

Part of the Central Data scsiTerminal ServerTM family, the ST-1016 is a convenient way to add high-performance serial expansion to UNIXTM workstations or PCs without consuming a card slot. A standard SCSI bus provides the host interface. This delivers a flexible, cost-effective solution for systems with limited provisions for expansion. The scsiTerminal Server / ST-1016 simply shares the SCSI bus with your existing disk and tape units.

Distinctive Characteristics

* Uses SCSI bus as interface to host computer * 16 asynchronous serial ports with full modem control for dial-up lines, terminals, printers, or plotters * Expandable to 112 serial ports off a single SCSI bus * Software compatible with all other scsiTerminal Server models * Fully compliant with SCSI/ANSI X3.131-1986 specification * SCSI-2 compatible; conforms to the SCSI Common Command Set as a SCSI communications device * 16MHz 80C186 CPU for interrupt control and timers as well as SCSI DMA support * 512K of zero-wait-state DRAM for plenty of buffer space * NCR 53C94 SCSI controller for fast, low-overhead SCSI service * Complete, easily installed driver packages offered at no charge for many of today's most popular versions of UNIX * Complies with FCC Class A and VDE-B requirements


The scsiTerminal Server / ST-1016 represents a new alternative in multiport expansion. It provides the capability of adding from 16 to 112 RS-232 devices to UNIX systems using one of the most accepted standards in the computer industry -- the SCSI bus. Using SCSI as the interface allows systems to be expanded without consuming any internal card slots.

Functional Description

The scsiTerminal Server / ST-1016 uses the industry-standard NCR 53C94 Enhanced SCSI Bus Controller to provide a high-performance interface to the SCSI bus. Data transfer rates up to 3.2MB/second are possible, which far exceed the total data throughput possible with even 16 asynchronous channels. Signetics 2698 Octal UARTs provide the high-density interface to 16 asynchronous channels. Full modem-control signals (RTS, CTS, DTR, DSR, and DCD) are supported for all lines. All ports are adjustable from 50-57.6K baud. The 16MHz 80C186 Highly Integrated Embedded Controller provides the processing power as well as refresh, timers, DMA, interrupt control logic, and chip select decode. The FastAsync firmware conforms to the Common Command Set definition of a SCSI communications device. The actual format of the commands is tailored to the unique needs of terminal handling, with a paramount emphasis on efficiency. A simple packetizing protocol allows multiple lines to be serviced with each SCSI transaction, thereby minimizing CPU overhead and bus loading. The firmware provides for a large amount of input and output buffering, automatic handling of flow control (both XON/XOFF and RTS/CTS), and full control over modem signals. A UNIX operating system driver is provided free of charge. Each driver comes complete with test and benchmarking programs and is easily installed. They are provided on either 3.5" or 5.25" floppy diskettes (or DAT for some systems). Drivers are also made available on QIC-150 tape for a nominal media charge.


CPU: Intel 80C186 at 16MHz, provides DMA control, interrupt control, refresh, timers, and chip-select generation. DRAM: 512K bytes at zero wait-states EPROM: Two 27256 EPROMs at zero wait-states SCSI: Single-ended interface using NCR 53C94 SCSI Bus Controller, 4.0MB/second asynchronous or 3.2MB/second synchronous data transfer rate RS-232 Serial: Signetics 2698 UARTs with 1488/1489 line drivers/receivers provide baud rates from 50 to 57.6K baud. Modem control signals supported: CTS, RTS, DTR, DSR, and DCD. DB-25 female connectors, DTE pinout. Power: +5V DC, 700mA maximum, 600mA typical 12V DC, 100mA maximum (fully loaded), 1mA typical (unloaded) Dimensions: 8.1" (20.6 cm) wide, 11.05" (28.5 cm) deep, 1.2" (3.1 cm) high

Ordering Information

ST-1016 SCSI Terminal Server Includes sixteen RS-232 DTE serial ports, power supply, external SCSI-2 terminator, UNIX device driver software, and appropriate SCSI cable.

SA-0002 SCSI-2 external terminator

Ordering Tips: A UNIX driver is provided with each unit. When ordering please specify the UNIX version and media type you prefer.

scsiTerminal Server is a trademark of Central Data Corporation. UNIX is a registered trademark of AT&T. The scsiSystems Company is a service mark of Central Data Corporation. 11/91

If you have any questions you may call our toll-free number 800-482-0315, or 217-359-8010.


From: (Tom Rushworth )

We just got one. We've had it installed for about 3 days, so there isn't a lot of history, but I can at least compare it to the Sun Sbus (SPC) card. (Central Data's server is called the STS.)

Configuration: SS2 clone running SunOS 4.1.2 scsiTerminal Server 1008+, drivers linked into kernel, not dynamic with: - 2 Telebit modems at 19.2k - 1 ZyXEL modem at 19.2K - 1 postscript printer at 19.2K - 1 high-speed pen plotter at 19.2K - 1 Xerox laser printer on the parallel port - terminals at 9600 on remaining ports

Performance: Interrupts/Sec for 1 uucp transfer (from perfmeter, very rough) 300-400 (vs 3,000! for the SPC) Bytes/Sec for uucp transfer (from log files) (tty[yz]* is Sun's SPC, tty[cC]* is Central Data's) `[ttyz01]->' bytes=2543403 secs=2650.372000 `[ttyy01]->' bytes=57393 secs=68.518000 `[ttyz00]->' bytes=596640 secs=396.485000 `[ttyy00]->' bytes=203100 secs=132.881000 3400536 / 3247 = 1047 bps outgoing ------ `[ttyz00]<-' bytes=6032773 secs=5115.424000 `[ttyy00]<-' bytes=7383749 secs=6491.499000 `[ttyy01]<-' bytes=60873 secs=81.625000 13477395 / 11688 = 1153 bps incoming --------- `[ttyc1]->' bytes=22608 secs=13.265000 `[ttyC1]->' bytes=289800 secs=184.847000 312408 / 198 = 1578 bps outgoing --------- `[ttyC1]<-' bytes=655700 secs=541.846000 `[ttyc1]<-' bytes=4532524 secs=3561.649000 5188224 / 4104 = 1264 bps incoming I haven't had it running long enough to get data on running 2 modems at once, the one time I saw it happening all I noticed was that I/s for 2 was less than twice I/s for 1. The load the STS presents for 1 uucp transfer seems to be (very roughly) 1/10th the load the Sun SPC board presents.

The installation guide that came with it has a small table of approximate performance numbers (they are careful to say your milage may vary :)) -

8 lines, 9600 baud, full duplex 1904 c/s/l 8 lines, 19.2K, primarily unidirectional 1905 c/s/l (either direction) 8 lines, 38.4K, output only 3264 c/s/l 8 lines, 38.4K, input only 3763 c/s/l 4 in, 4 out, 38.4K 3763 (in) 1536 (out)

An unexpected bonus we got is that it handles a paper-out condition on the parallel port in a graceful way (it just pauses (with NO message) until you fill the printer). The Sun SPC card gets a ppc_acktimeout, so lpd aborts and reprints the job (which makes it fun trying to print a job bigger than the printers paper supply).

One final plus - the RTS/CTS flow control really works, *both* ways, which makes using the modems ever so much more pleasant...

---------------- From: Pete Hartman <>

Well, I have a mixed tale.

I have had a good response from their support people when I've had problems and the time to figure them out. I spent a long time not realizing I had misconfigured ours (we have two connected to a SS-2, which are used for incoming lines from an AT&T serial network called ISN), and trying to get them to help me when I didn't even understand what I was doing quite right. They tried hard. But it took me understanding what I should be doing (the lines had to be configured as if they were modems, so that they would pay attention to Carrier Detect) before I solved some basic problems.

Since then (only a few months) I find that they intermittently stop working. Getty's run on these ports, there don't appear to be processes hung on the ports, but they don't answer. I don't understand the problem and haven't taken the time to chase it down (we have alternate means of connecting to that machine, and I'm responsible for 30-odd more suns, some with users who are a lot more strident about what needs to be done for them). I assume that when I do, I can get good help, but until then, they still don't work quite right.

----------------- From: (C. R. Oldham)

I was going to buy one--as it was quite cost-competitive with Sun's ALM-2 board, but Central Data informed me that the scsiTerminal server would not function with my SPARCserver 4/470. Something about incompatibilities in Sun's SCSI interface for this machine.

----------------- From: (Mike Busby)

We have been evaluating using the Central Data Terminal server for SLIP/PPP use internally on Sun/Solbourne. The limited tests I ran indicated that it could handle the load at 56 kbaud using Telebit Worldblazer modems. It also handled hardware flow-control correctly. We tried both modems and hard-wired connections. The model we tested was the ST-1016.

One minus was that they will not support Solbourne until they conform to SCD 1.1 and SCSD (Sun common SCSI definition) compliance. I don't believe that this will happen until Solbourne goes to Solaris 2.X.

----------------- From: (Mike Andrews)

We have the SP-1003 parallel version. Does it work? We just got a second one!

The only problem we've had is with it not initializing at boot time. Watch carefully to see that it is creating the ports in /dev when the device is initialized. (We actually only had that problem once, but since we have it on our main server, it was pain to have to reboot it.)

I have called Central Data for support and had no complaints.

We drive several network printers via parallel extenders. The high speed port works at about 215000 bps, not as fast as a Ethernet printer server but still great and much less costly.

The device dirver is easy to install and very intelligent. It will find all of the Central Data Servers on *any* SCSI bus at boot time and configue /dev devices in sequence to use the ports.


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