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In this page: [Optimal Settings]  [Switch Position]  [Adapter ROM Address]  [Interrupt]  [I/O Port]  [Shared RAM Size]  [Data Rate]  [Unit prefixes]


IBM Token Ring Adapter 4/16

Switch Settings

IBM Token Ring Adapter 4/16 (thumbnail) Closeup of switch bank on IBM Token Ring Adapter 4/16 (thumbnail) The standard ISA IBM Token Ring Adapter has a switch bank of 12 switches. On an IBM computer running a DOS or Windows 3.1 environment where the address range from E000-EFFF is used by the BASIC ROM and the address range F000-FFFF is used by the system BIOS ROM, the optimal settings for the Token Ring Adapter RAM is at DC00-DFFF and ROM is at DA00-DBFF. For clone PCs that have no BASIC ROM it would be better to place the adapter RAM and ROM as low as possible. The exact location depends on whether there is Video ROM present. It is even possible to tuck the adapter RAM and ROM in an unused video text area. Since most computers have a colour monitor, this is most likely the monochrome text area at B000-B7FF. The same settings can be used for the Microchannel IBM Token Ring Adapter 4/16 A, but the settings are configured with the reference utility, not switches on the adapter.

These ROM locations are not documented in the manual packed with the IBM Token Ring card. In fact, the function of the switches to set memory locations aren't documented there. I have determined the switch functions by comparing the bit patterns of the two high-order bytes with the documented ROM locations, and extrapolated the function of the remaining settings from there. The behaviour of the card is consistent with these values, but neither I (Bob Jonkman) nor SOBAC Microcomputer Services will be responsible for any failures incurred through the use of the switch settings documented here.

Only the Adapter ROM address can be set with switches on the Token Ring Adapter. The Shared RAM location is specified by a parameter on the command line of the token ring driver, or a configuration file. Some drivers (like TOKEN.LAN for a Netware server) will not allow alternate configurations, and expects the Shared RAM to be at the default D800-DBFF. In this case you should also configure the Adapter ROM to be at the default DC00-DDFF.

Note that the Adapter ROM Address table is not exhaustive, but only lists the most common settings. All addresses in this document refer to segment addresses in upper memory (above 640 KibiBytes, below 1 Mebibyte).

The following switch settings have been designed to optimize upper memory where E000-FFFF is unavailable. A NET.CFG file for these settings is available for workstations on a Novell Netware network. The memory addresses in NET.CFG refer to absolute addresses, not segment addresses, hence the extra zeroes.

^ Optimal Switch Settings
ROM Address Interrupt I/O Port Shared RAM Data Rate
Switch number 1 2 3 4 5 6 7 8 9 10 11 12
Optimal OFF ON OFF OFF ON OFF ON ON OFF OFF ON OFF
AROM=DA00-DBFF IRQ=2 I/O=A20 (PRI) ARAM=16 KibiBytes 16 Mib/s
IBM Default OFF ON OFF OFF OFF ON ON ON OFF ON ON ON
AROM=DC00-DDFF IRQ=2 I/O=A20 (PRI) ARAM=8 KibiBytes Mib/s

The following tables list the functions and common settings for each set of switches.

^ Switch Position
OFF ON
UP DOWN

^ Adapter ROM address
1 x x x x x x 0 Bit Pattern of First Two Digits of Upper Memory Segment
OFF=1, ON=0
1 2 3 4 5 6 Switch Position
ON OFF OFF OFF OFF ON B400-B6FF "Mono Text"
(16K Shared RAM should be set to B000-B3FF)
Used when the Monochrome Text area is available, 
no monochrome monitor will be attached to the system
OFF ON ON ON OFF ON C400-C5FF "Low Cxxx"
(16K Shared RAM should be set to C000-C3FF)
Used when no Video ROM is present
OFF ON ON OFF OFF ON CC00-CDFF "Video Cxxx"
(16K Shared RAM should be set to C800-CBFF)
Used when Video ROM=C000-C7FF
OFF ON OFF OFF ON OFF DA00-DBFF "High Dxxx"
(16K Shared RAM should be set to DC00-DFFF)
OFF ON OFF OFF OFF ON DC00-DDFF "IBM Default"
(16K Shared RAM default is D800-DBFF

^ Interrupt
7 8 Switch Position
ON ON IRQ=2
ON OFF IRQ=3
(usually COM4)
OFF ON IRQ=6
(usually Floppy Drive)
OFF OFF IRQ=7
(usually LPT1)

^ I/O Port
9 Switch Postion
OFF A20 (Primary)
(this setting conflicts with the standard audio card I/O port of 220
set your audio card to an alternate I/O port)
ON A40 (Secondary)

^ Shared RAM size
10 11 Switch Position
ON ON 8 KibiBytes
OFF ON 16 KibiBytes
ON OFF 32 KibiBytes
OFF OFF 64 KibiBytes

^ Data Rate
12 Switch Position
ON 4 Mib/s
OFF 16 Mib/s



^ What are these units?

This article now uses the terms "Kibibyte" and "Mebibyte". These units use the prefixes "Ki" (or "Kibi", short for "kilo-binary") to represent 210 (or 1024) and "Mi" (or "Mebi", short for "Mega-binary") to represent 220 (or 1,048,576). This reduces the ambiguity for computer-related terms, since the SI prefix "k" or "kilo" actually means 103 (or 1000) and "M" or "Mega" actually means 106 (or 1,000,000).

See the Wikipedia entry for Byte/Prefixes for a list of all the binary prefixes.


In this page: [Top of Page]  [Optimal Settings]  [Switch Position]  [Adapter ROM Address]  [Interrupt]  [I/O Port]  [Shared RAM Size]  [Data Rate]  [Unit prefixes]

Related pages: [Token Ring specifications]  [NET.CFG] [IBM] [IBM Networking | Token-Ring Adapters] [Novell

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All text and pictures Copyright © 1998-2002 SOBAC Microcomputer Services unless otherwise attributed

This page was last updated on Sunday, 13 October 2002 by Bob Jonkman

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