From the Lists...
Summary of responses to Multi-port serial card survey

From: Duncan Bennett <>

On the 4th of August 1995 I posted the question to linux-uk-help:

Can anyone recommend a multi-port serial card that works well with Linux? I'm thinking of something less than 8 ports that will not need to handle speeds greater than 9600 baud.

Here is a summary of the responses as promised: wrote:

Not sure that I strictly /recommend/ it but ... I finally got a quad port card as manufactured by Brain Boxes of Liverpool, having drawn blanks on a long series of enquiries round the country for a 4-port card (with 16550B chips it cost about 120 pounds). This does not work quite like the AST 4-port for which the Linux kernel has long had built-in support (the interrupt status register is offset by 8 bytes from the base address, compared with 7 bytes for the AST), and I have not been able to find a driver for it so as to use it in shared-interrupt mode. It is claimed to be 100% Digiboard PC/4 compatible, but I have not been able to find this driver for Linux either.

On the other hand, it is fairly straightforward to set it up to use 4 different interrupts, so this is what I did and it works (and I have no interrupts left now).

/etc/rc.d/rc.serial needs the lines (or similar):

SETSERIAL="/bin/setserial -b"
$(SETSERIAL) /dev/ttyS4 uart 16550A port 0x180 irq 10 -- -fourport
$(SETSERIAL) /dev/ttyS5 uart 16550A port 0x188 irq 11 -- -fourport
$(SETSERIAL) /dev/ttyS6 uart 16550A port 0x190 irq 12 -- -fourport
$(SETSERIAL) /dev/ttyS7 uart 16550A port 0x198 irq 15 -- -fourport
Brain Boxes are at Unit 3F, Wavertree Boulevard South, Wavertree Technology Park, Liverpool L7 9PF. Tel: 0151-220-2500; Fax: 0151-252-0446. (Graham Biswell) wrote:

I haven't had any personal experience with such cards, but from what I have seen, the Cyclades cards are well supported, & are cheap. They advertise in Linux Journal, & can be email'd at

Look through comp.os.linux.hardware & read the Serial HOWTO, for some more ideas. The latter suggests:

   2.  Supported serial hardware
   Linux supports the following serial hardware, (ie is known to work

   o  standard PC serial boards (COM1 - COM4)
   o  standard PC internal modems (COM1 - COM4)
   2.1.  Multiport serial boards
   o  Usenet Serial Board II
   o  Boca 4-port (BB-1004)
   o  Boca 8-port (BB-1008)
   o  Boca 16-port (BB-2016)
   o  Boca 6-port (IO/AT66)
   o  AST FourPort boards and clones
   o  Accent Async boards
   o  Bell Technologies HUB6
   o  STB-4COM
   In general, Linux will support any serial board which uses a 8250,
   16450, 16550, 16550A (or compatible) UART, or an internal modem which
   emulates one of the above UARTs.
   Special note on the BB-1004 and BB-1008, they do not support DCD and
   RI lines, and thus are not usable for dialin modems.  They will work
   fine for all other purposes.
   2.2.  Intelligent multiport serial boards
   o  Cyclades Cyclom 8-port (Cyclom 8Y)
   o  Cyclades Cyclom 16-port (Cyclom 16Y)
   o  DigiBoard PC/Xe (2, 4, or 8 port) (expected November 1994)
   o  Digiboard COM/Xi (4 or 8 port)
      (pre-ALPHA driver contact Simon Park  for
   o  Specialix SI0 (modular, 4 - 32 ports)
      (ALPHA driver: contact Simon Allen 
      for information) (Martin Houston) wrote:

I use a Longshine 4 port - it is an AST 4 port clone with 16550 chips. It has always worked fine for me - I run a high speed modem, mouse and printer off it at the same time. The price is very good - only about 30-40 quid! (Tim Jones) wrote:

Comtrol Corporation manufactures a range of multiport cards, the most recent of these being the RocketPort, which was reviewed in a recent Linux servey of multiport boards. The conclusions drawn from this survey were that the RocketPort was the best card on the market.

When installed in a 16-bit ISA or EISA slot of a PC, RocketPort transmits and receives a significantly greater amount of data which enables more work to be accomplished in a much shorter period of time. In addition, host CPU utilisation is minimized to allow more system resources to be available for running existing software applications. This industry leading performance of up to 230Kbps full duplex across 32 ports simultaneously is the result of RocketPort's unique design features including: Dedicated on-board 36MHz processors - one for every 8 ports to ensure consistent application of power to each port, I/O mapping to eliminate memory mapping conflicts, and the use of proprietary Application Specific Integrated Circuits (ASICs) to yield the most reliable serial I/O performance.

The price for an 8 port RocketPort Octacable board is 360 pounds. Resellers can contact us for details on discounts etc.