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comp.arch.bus.vmebus Frequently Asked Questions (FAQ)

This posting contains a list of Frequently Asked Questions and other information about the VMEbus computer system. The VMEbus is an industrial grade open systems bus specification. This FAQ contains general information about the VMEbus and VXIbus specifications, where to obtain further information and answers to questions often asked on comp.arch.bus.vmebus.
Archive-name: computer-arch/bus/vmebus-faq
Posting-Frequency: monthly
Last-modified: 1996/01/05
Version: 9.0

                      Frequently Asked Questions

                      This list is maintained by:
                              Robert Boys
                         San Jose, California
                  formerly of Guelph, Ontario, CANADA


                           January 05, 1996
                              Version # 9

=                                                                     =
=    I am finally updating this FAQ !  I have been fairly busy. :-)   =
=                                                                     =
=   I hope all of you reading this, your families and friends had a   =
=   wonderful and peaceful Christmas and New Year holiday wherever    =
=   you may happen to live in the world.  I wish that all of you      =
=   have a continuing prosperous and safe 1996.                       =
=                                                                     =
=  As you may have noticed in my header - I have moved from the land  =
=  of ice and snow (Canada) to sunny California.                      =
=  I now work for Hitex Development Tools - aka HiTOOLS Inc.          =
=  They sell emulators and such.  Watch for me at trade shows.        =
=  VMEbus, M68K and HC11 info may now be sent to      =
=                                                                     =
=  I have a new Homepage- in California   =
=  The latest version of this FAQ will be stored there - i.e. the     =
=  "work in process" version.  I will be getting the site running     =
=  in the next few weeks.  This is also true for the FAQ for the M68k =
=  My backup Homepage is in Canada       =
=                                                                     =
=   This FAQ is also stored on:                                       =
=  (California)         =
=  (Germany)      =
=     (Western Canada)    =
=                                                                     =
= You can get this entire FAQ with graphics by pointing your browser  =
=   at the indicated Web pages and looking for the file   =
=                                                                     =

The information contained in this FAQ is believed to be correct and up
to date.  Every effort has been made to ensure accuracy.  The maintainer
cannot be responsible for errors and omissions.  This article is
copyright (c) 1996 and all rights are reserved. 
This article may be reprinted provided it is intact, proper credit is
given and no cost is levied.  Contact the author for permissions.

What's New!       new parts are indicated with a ]

*    US$150 C compiler offer from Introl Corp (non-commercial license)
     is now available in a Windows 95 version.

*    John Black's book - The Systems Engineer's Handbook is now only $60

*    Test & Measurement World magazine now has VXIbus information.

*    The VME64 mailing list has a new address.


1)   The USENET Newsgroup comp.arch.bus.vmebus

2)   The VMEbus - Technical Information
          A)  The VMEbus - Introduction
          B)  The VMEbus - Description
          C)  DIN Connector Assignments
          D)  VME64 - a new standard

3)   The VXIbus - Technical Information
          A)  The VXIbus - Introduction
          B)  The VXIbus - Description
          C)  DIN Connector Assignments

4)   Information Sources
          A)  VMEbus Systems Magazine
          B)  VXI Journal
          C)  Real Time Engineering
          D)  Micrology pbt, Inc.
          E)  VITA - VMEbus International Trade Association
          F)  Computer Design
          G)  Test & Measurement World
          H)  The Manufacturers
          I)  Unadvertised ftp and WWW Sites

5)   Answers to Frequently Asked Questions
          A)  Newbridge Microsystems
          B)  Battery Clocks - MK48TO2B-xx
          C)  Where does the name "VME" come from?

6)   Profiles


1)   The USENET Newsgroup comp.arch.bus.vmebus
The questions that appear on this newsgroup generally pertain to
specific technical questions that are beyond the scope of a FAQ, about
where to locate information about the VMEbus, where to find boards to
perform specific functions or the addresses of VMEbus manufacturers. 
Many manufacturers of VMEbus equipment and associated products and
services monitor this newsgroup on a regular basis.  They include:

Motorola            Newbridge                EKF Elektronik
Heurikon            VITA                     Micrology pbt
DY 4                RadiSys                  Schroff, Inc
VMIC - VME Microsystems International Corp.
Radstone Technology PLC (UK)                 Themis Computer
Titan Electronics (San Diego)                et al
your firm name here (email me)

The latest version of this FAQ is archived at:
or  (California)  (Germany)
The working copy is on my Homepage -

You can retrieve the entire HTML FAQ with the .gif files by pointing
your browser at the above sites and look for

2)   The VMEbus - Technical Information

A)  The VMEbus - Introduction
VMEbus modules are state of the art products and are used to construct
very powerful and rugged computer systems. The VMEbus is an industrial
open standard system.  VMEbus boards have data bus sizes of 16, 32 or 64
bits and are designed to be plugged into a backplane that has up to 21
slots for other boards.  These other boards can be CPU boards or
peripheral boards providing various functions.

The VMEbus standard originated with the Motorola VERSAbus in 1979 which
was designed using the then new MC68000 microprocessor.  The VMEbus
signals are patterned after the M68000 bus signals and timing.  VMEbus
boards now contain processors such as DEC Alpha, MIPS, i960, various DSP
chips, AM29000 (RISC chip), PowerPC and 80486 in addition to the
Motorola 680x0 line.  Many peripheral boards exist including VGA,
telecommunication, analyzers, data acquisition, video processors and
memory (1 gigabyte!).  The VMEbus originated in 1981.

The VXIbus is an instrumentation bus compatible (sort-of) with the
VMEbus.  The VMEbus specification specifies the physical dimensions of
the boards, backplane and the chassis as well as the electrical
specifications of the bus and various communication protocols.

In addition to the VMEbus, the VXIbus and Futurebus+ will be covered in
this document in the future.

A PMC (PCI Mezzanine Card) is a proposed IEEE specification for a low
profile mezzanine expansion bus for VMEbus, Multibus II and Futurebus+
systems.  It has a 32 or 64 bit bus and has the same electrical
specifications as the PCI bus (Peripheral Interconnect Bus).

There are over 200 vendors supplying products to the VMEbus community. 
VMEbus suppliers are most active in the USA, Germany and Canada and
range from large corporations to small custom shops.  Specifying a
VMEbus system releases the user from the expensive, time consuming and
sometimes (often) risky business of in-house hardware design.

Information resources for the VMEbus come mainly from three sources:
VITA, the VMEbus Systems Magazines edited by John Black and the
manufacturers.  All prices quoted are in US dollars.

B)  The VMEbus - Description
A VMEbus board can be either single or double height.  A single height
board is 100mm x 160mm with one 96 pin DIN 41612 connector called P1 on
the rear that plugs into the backplane.  A double height board is 233mm
x 160mm and may have a second 96 pin DIN connector named P2.  A single
height board is also known as a 3U and a double height a 6U.  There are
9U boards in existence but they are not part of the VMEbus
specification.  The front edge or face of a typical board is 20mm wide
and may incorporate RS-232 connectors, indicator lights and switches.

The backplane can have up to 21 slots providing the J1 connectors for
the boards to plug into.  The J2 connectors (if required) can be
supplied with a second backplane board or in one piece with both J1 and
J2 connectors.  A J1 (on the backplane) matches to a P1 (on the board)
and a J2 to a P2.  The spacing between slots is 20.32 mm (0.8 inches).

Power is supplied to the VMEbus board through P1 and P2 (if used).  The
DIN plugs used are arranged in three rows (A, B, C) of 32 pins on 0.1
inch centres.  These plugs are approximately 0.85 mm wide and 84 mm

P1 supports 16 and 24 bit addressing and 8 and 16 bit data paths.  P2
uses the centre 32 pins to support full 32 bit data and addressing
paths.  The two outer rows of P2 are user defined and are used for i/o
ports, disk drives and other external peripherals.

C)  DIN Connector Assignments
J1/P1 Pin                                                J2/P2 Pin
Assignments                                              Assignments
Pin #     Row A       Row B          Row C               Row B

1         D00         BBSY*          D08                 +5v
2         D01         BCLR*          D09                 GROUND
3         D02         ACFAIL*        D10                 RESERVED
4         D03         BG0IN*         D11                 A24
5         D04         BG0OUT*        D12                 A25
6         D05         BG1IN*         D13                 A26
7         D06         BG1OUT*        D14                 A27
8         D07         BG2IN*         D15                 A28
9         GROUND      BG2OUT*        GROUND              A29
10        SYSCLK      BG3IN*         SYSFAIL*            A30
11        GROUND      BG3OUT*        BERR*               A31
12        DS1*        BR0*           SYSRESET*           GROUND
13        DS0*        BR1*           LWORD*              +5V
14        WRITE*      BR2*           AM5                 D16
15        GROUND      BR3*           A23                 D17
16        DTACK*      AM0            A22                 D18
17        GROUND      AM1            A21                 D19
18        AS*         AM2            A20                 D20
19        GROUND      AM3            A19                 D21
20        IACK*       GROUND         A18                 D22
21        IACKIN*     SERCLK*        A17                 D23
22        IACKOUT*    SERDAT*        A16                 GROUND
23        AM4         GROUND         A15                 D24
24        A07         IRQ7*          A14                 D25
25        A06         IRQ6*          A13                 D26
26        A05         IRQ5*          A12                 D27
27        A04         IRQ4*          A11                 D28
28        A03         IRQ3*          A10                 D29
29        A02         IRQ2*          A09                 D30
30        A01         IRQ1*          A08                 D31
31        -12V        +5V STDBY      +12V                GROUND
32        +5V         +5V            +5V                 +5V
1)  J2/P2 Rows A and C are user defined.  They are specified in the
VXIbus which is one reason why the VXIbus and VMEbus are not totally

2)  A01 to A31 is the address bus.  Notice it is similar to the MC68000
scheme ie without A0.  DS0* and DS1* (DS = Data Strobe) specify the
upper or lower portion of the data bus. (rather than having a A0)  See
the FAQ for comp.sys.m68k for a discussion of this issue.

3)  * means an active low signal.

D)  VME64 - a new standard
The regular VMEbus standard accommadates 32 bit address and data buses. 
Data transfers are 32, 16 and 8 bytes wide.  One type of data transfer,
called a Block Transfer, allow up to 256 bytes to be transferred with
only the start address placed on the address bus once.  For the rest of
the transfer, the address bus is idle.  The VME64 standard utilizes this
unused bandwidth to enable 64 bit block transfers.  The lower 32 bits
are placed on the regular D0 to D31 and the upper 32 bits placed on the
idle address bus A01 to A31.

The VME64 standard adds many other advanced features.  VME64 is a VITA
Standard.  This standard, which has recently gained ANSI approval, is
backwards compatible with existing VMEbus boards.
For more information:

There is a VME64 Reflector (mailing list).  To subscribe Email to leaving the subject line blank with the following
command in the body of the message:    subscribe vita
You will receive a confirmation of your subscription and to address
Email to others on the list send your message to

3)   The VXIbus - Technical Information

A)  The VXIbus - Introduction
The VXIbus is an instrumentation bus based on the VMEbus, the Eurocard
and standards such as IEEE 488.2 and the HP GPIB (General Purpose
Instrumentation Bus).  It is an open architecture and is useful for
automated test systems and data collection.  The issue of
electromagnetic radiation is part of the VXIbus specification.  VXIbus
is an acronym for "VMEbus eXtensions for Instrumentation".  The VXIbus
was announced in 1987.

The VXIbus expands on the VMEbus so the two bus specifications are very
similar.  TTL and ECL trigger lines, a local bus and an analogue summing
bus are among the added features.  The December 1988 issue of "VMEbus
Systems" contains a good outline of the VXIbus.  The Spring 1995 issue
of "VXIjournal" is a VXIbus Buyer's Guide.

B)  The VXIbus - Description

There are two more board sizes in addition to the VMEbus single and
double sizes:

Size      Height    Dimensions (mm)     Connectors          Slot Spacing
----      ------    ---------------     ----------          ------------
A         Single    100 x 160           P1                  0.8 inch
B         Double    233 x 160           P1 & opt P2         0.8 inch
C         Double    233 x 340           P1 & opt P2         1.2 inch
D         Triple    366 x 340           P1, opt P2,P3       1.2 inch
opt = optional
P1, P2 & P3 are the same 96 pin DIN connector as in the VMEbus.
The increased width of the C and D sizes are to accommodate thick
analogue modules and EMI shielding.

The VXIbus uses the same pin assignments on P1 and the centre P2 pins as
the VMEbus.  The two rows (A & C) on P2 that were user defined on the
VMEbus are assigned on the VXIbus.  Features added include ECL (emitter
coupled logic) and TTL trigger signals, a 10 Mhz ECL clock, more supply
sources (+-24, -2 and -5.2 volts), an analogue summing bus, local bus
lines and a module identification line.  The optional P3 available on
the D size board offers the same type of resources as P2 but at a speed
of 100 Mhz (P2 is only 10 Mhz).

Reasons why the VMEbus and the VXIbus specifications are not totally
compatible include:

  1)  conflicts may arise depending on the use of the A & C rows on P2.
  2)  VMEbus Double height boards are not as deep as VXIbus size C.
  3)  The VMEbus has no configuration registers while the VXIbus does.

A VXIbus system can have up to 13 modules consisting of a central timing
module in Slot 0 and a maximum of 12 additional instrumentation modules.

C)  DIN Connector Assignments
P1 and P2-B (the centre row) have the same pin assignments as the VMEbus
and are listed above.  The outside 2 rows of P2 are specified in the
VXIbus.  In the VMEbus specification, these two rows are user defined. 
Since Slot 0 on the backplane is reserved for a system timing module,
P2-A has slightly different assignments than for Slots 1 to 12.  P2-C
has essentially the same assignments for all slots.

          to be continued.....

4)   Information Sources

A)  VMEbus Systems Magazine
25875 Jefferson               (Advertising and Business Offices)
St. Clair Shores              The Editorial Offices are at Micrology
Michigan, 48081               listed below.
(313) 774-8180
(313) 774-8182 (FAX)

This magazine is free to qualified VMEbus systems users and specifiers
in the United States and Canada.  There is a subscription fee applicable
for other countries.  This magazine contains industry news, informative
articles and useful advertisements.  Back issues are available from
Micrology.  For more information see
The December 1994 issue is a useful Buyer's Guide.

B) VXI Journal
Business Offices              Editorial Offices
----------------              -----------------
25875 Jefferson               11051 Pinto Drive
St. Clair Shores              Fountain Hills
Michigan, 48081               Arizona, 85268
(313) 774-8180                (602) 837-3756
(313) 774-8182 (FAX)          (602) 837-3768 (FAX)
Email address:

Published by the people at the VMEbus Magazine at the same addresses.
Subscriptions are free to qualified users of the VXIbus or GPIB in
Canada or the USA.

C) Real Time Engineering
A new magazine, Real Time Engineering, is also published by Micrology in
Arizona.  The Spring 1995 edition is a Buyer's Guide.

To get a subscription request form for any of these magazines, send
Email to John Black, Editor ( or contact the offices
in Michigan.

The World Wide Web (WWW) site for these three magazines is:

D)  Micrology pbt, Inc.
2618 S. Shannon Drive
Tempe, Arizona  85282
(602) 967-5581
(602) 968-3446  (FAX)
(602) 968-9265  (Real Time Engineering Magazine)     John Black

A VXIbus Buyer's Guide - $33

Back issues of VMEbus Systems Magazine are available for $4 each.
Email and request a listing.

*** Micrology is having a sale on some back issues** (still??)

The Systems Engineer's Handbook:
A guide to building VMEbus and VXIbus systems:

John Black has edited this hard cover text that covers the VMEbus and
VXIbus thoroughly.  This is an easy to read book that contains the
complete VMEbus and VXIbus specifications and information on graphics,
disk interfaces, Ethernet, image processing and interfacing to external
devices such as stepping motors...and much more.
]It is now available direct from Micrology for US$59.95 + $7 shipping.
Phone (602) 966-5936   FAX  (602)-968-3446   Email -

E)  VITA - VMEbus International Trade Association

VITA                                         VITA Europe
10229 North Scottsdale Rd                    P.O. Box 192
Suite B                                      5300 AD Zaltbommel
Scottsdale, Arizona 85253                    The Netherlands
(602) 951-8866                               31.4180.14661 (or .16593)
(602) 951-0720 (FAX)                         31.4180.15115  (FAX)

John Rynearson                               Zoltan Hunor
Technical Director                           Director VITA
VITA USA                                     Europe                   

World Wide Web site:

VITA is the world-wide association of the VMEbus users and manufacturers
and as such organizes global promotion of the VMEbus including
exhibitions, seminars and courses.  Vita does not test and approve
components but is a full member of ANSI and promotes standards of
interest to the community.  VITA publishes various magazines and manuals
about the VMEbus.
In Europe, VITA has a mailing list of 100,000 engineers.

VMEbus Handbook          $53
VMEbus Specification     $32

The Handbook provides information for programmers, system integrators,
engineers while the VMEbus Specification provides more "hardware level"
information such as that needed for board design.  These two books
provide the information needed to understand the VMEbus system and are
worth the moderate cost.

VITA also publishes a Buyer's Guide for $55 (or $110 a year).  

VITA now offers a quarterly news publication, the VITA Journal, on a
complimentary subscription basis.  It contains member and industry news
and the activities of the VITA Standards Organization.
F)  Computer Design
Computer Design is amagazine that contains VMEbus advertisements with
articles about computer design in general.  It is free to qualified
readers by contacting Ron Kalusa at

G)  Test & Measurement World
This magazine will feature the VXIbus starting in January 1996.  The
February issue will feature an article on using VMEbus slave cards in a
VXIbus system.  It is free to qualified industry personnel.

275 Washington Street
Newton, Massachusets  02158
Phone  (617) 558-4671
Fax    (617) 558-4470

H)  The Manufacturers
There are many manufacturers of VMEbus computer modules worldwide. 
Refer to any of the Buyer's Guides listed above or post to
comp.arch.bus.vmebus for more information.  Many manufacturers are
getting Internet Email addresses.  They note them in their
advertisements in the magazines listed above.

Many VMEbus CPU boards have a built-in monitor program similar to the
TUTOR monitor and have a RS-232 port that can be hooked up to a terminal
or a host computer.  Programs can be entered with the provided simple
assembler/disassembler and executed.  Peripheral devices can be attached
easily to these boards.  These boards are often available used and the
older ones with 68000/10 CPUs have a low cost(<$50) and this is a good
way to become acquainted with the VMEbus.  See the FAQ for comp.sys.m68k
for more information.

I)  Unadvertised ftp and WWW Sites

     (Motorola BBS)
     (for html)
 ( (AESOP & DR. BUB) 
 - info on MC68302 and 68360.  
There are many links between each of these sites.
DR. BUB (DSP information) is not operational yet.

VITA                     -

Heurikon                 -
                                        (nifty daily cartoons)
Dallas Semiconductor     -
                                        (Postscript data sheets)
Maximum Strategy Inc.    -  (disk arrays)

]Hitex Corporation - for California
                         In-circuit emulators and remote debuggers.
Titan Electronics

]Introl Corporation:

Introl is offering a non-commercial license for their US$2,000 C
compiler.  This is the full version - it is not crippled.  It comes with
an instruction manual.  See their homepage for more information.
This is now available in a Windows 95 version.

FAQ - comp.sys.m68k: for information on the Motorola M680x0 and MC683xx
--------------------  Germany  California  (also 8051, HC11 and PowerPc FAQs)

5)   Answers to Frequently Asked Questions

A frequently asked question is "are there any easy-to-use devices to
provide a VMEbus interface to my computer design?".  Two suppliers of
chips to do these tasks are Cypress and Newbridge .

A)  Newbridge Microsystems
The VME64 (SCV64) controller chip provides a 64 bit VMEbus interface
from the local bus.  This chip has a built-in DMA controller, VMEbus
address decoder and local bus burst modes.  It is a 299 pin PGA
($308CDN) or a 304 pin PQFP ($256CDN) package.

Newbridge also make PCI to VMEbus interface ("UNIVERSE")($US160 @ 1K)
and Futurebus+ interface chips ("LIFE").  A new part, "TROOPER" is a low
cost ($40 1995 @ 1K) slave-only VMEbus interface chip.  Available June
1995.  The SCV64 and "TROOPER" are fabricated by Motorola.

The "SPANNER" is now in production.  This is a MC68040 to PCI bridge
chip.  This is Newbridge's introductory offering in this area.

(800) 267-7231 (North America), (613) 592-0714 in Canada or
(408) 258-3600 in California.  

Email addresses: for general inquiries or for technical support.

<prices may be inaccurate>  The SCV64 (33 Mhz QFP) has been reported as
costing US$ 332 (qty=5), US$ 287 (25) and US$ 248 (100).

Cypress Semiconductor
Cypress manufactures a series of useful VMEbus integrated circuits:

VIC64     - an enhanced VIC068.   All the features of the VIC068 plus
          MBLT support.  (Multiplexed Block Transfer) Provides a direct
          connection to the M68K family and mappable to others.  VME64
          compliant (64 bit block transfers - rates up to 70
          mbytes/sec).  144TQFP, 144PPGA, 144CPGA, 160PQFP, 160CQFP. 
          $US 142 (Qty 100)

VIC068    - VMEbus Interface Controller - provides VMEbus controller
          functions between a CPU and the external VMEbus.  VMEbus
          SYSCON (system controller), interrupt handler, local DMA and
          a DRAM controller.  32/16/8 bit transfers.  144TQFP, 144PPGA,
          144CPGA, 160PQFP, 160CQFP.  $US 113 (Qty 100)

VAC068    - VMEbus Address Controller -  forms a complete VMEbus
          master/slave interface when used with the VIC068.
          144PPGA, 144CPGA, 160PQFP, 160CQFP.  $US 91 (Qty 100)

 CY7C960  - Slave VMEbus Interface Controller  - VME64 (64/32/16/8 bit
          data transfers), auto-slot ID, DMA, DRAM controller with
          refresh.  80 mbyte/sec Block Transfers.  CR/CSR support (used
          for Auto-slot identification to determine which slot a
          participating module is in).
          64TQFP, 64CQFP, 68CPGA.  $US 29

 CY7C961  - based on the CY960 - includes local and remote VMEbus Master
          capability. on-chip DMA.  100 TQFP, 100CQFP.  $US 47 (Qty 100)

CY7C964   - Bus Interface Logic Circuit - a companion part to the
          products listed above.  This 8 bit part is used to drive the
          upper three bytes of the VMEbus data and address buses.  Three
          devices are needed for VIC068 and VIC64 and four with the
          CY7C960/961.  The VIC64 and VIC068 directly drive the lower
          bytes.  The purpose of this part is to simplify the
          interfacing of the board logic by providing various counters,
          latches, comparators and drivers.
          64TQFP, 64CQFP, 68CPGA.  $US 19 (Qty 100)

       San Jose, California, U.S.A        Toronto, CANADA.
       Phone (408) 943-2600               Phone (416) 620-7276
       FAX   (408) 943-2741               FAX   (416) 620-7279                 Ed Dupuis (

       BBS: (408) 943-2954 (1200 to 19.2k, 8N1)  

B)  Battery Clocks - MK48TO2B-xx
Some VMEbus CPU boards contain a clock IC with an integral battery such
as the MOSTEK MK48TO2B-25.  The battery in this device is supposed to
last for five years, then the entire chip must be replaced.  It seems
nobody expected these boards to become obsolete at 5 years.

The MK48TO2B-25 is being discontinued and perhaps replaced by the
M48TO2-200PC1.  Mauser Electronics <(800) 346-6873 or (817)483-4422> nor
Arrow have any MK48Ts and the M48Ts have a delivery time of 8 to 14
weeks.  MOSTEK is apparently now owned by SGS-Thompson who will be
replacing the MK48TO2B with a 2 piece part called the "SnapHat".  The IC
proper and the battery/crystal are replaced separately.  This
information is provided by Gerry Belanger and Dennis Johnson.

Dallas Semiconductor makes the Timekeeper series of clock chips.  Their
US phone number is (214) 450-0448 or (800) 336-6933.  
The Dallas DS1642 may be replaced the Mostek MK48TO2B-25<not confirmed>. 
The DS1642 is available in speeds of 120 or 150 nsec.  It is available
directly from Dallas Semiconductor for about US$17 plus shipping with a
delivery time of 4 to 6 weeks.  Dallas suggests that Newark Electronics
may have this item in stock. (800) 463-9275 CANADA only.(?)

How to add an external battery:

The MK48TO2B-25 Mostek real time clock consists of a standard 24 pin DIP
with a black plastic cap attached to its top.  This plastic restangular
cap contains the clock crystal and the battery.

This cap is attached at each end only with some sort of potting material
that seems to be an epoxy.  If you put the MKT48 up to a light source
you should be able to see a gap between the plastic cap and the DIP. 
Notice that the cap is glued to the DIP only at the ends and then only
in the centre of the ends.  ie where the half-circle is molded into a
DIP to indicate where pins 1 and 24 are and at the corresponding place
at the other end.

The wires for the crystal and the battery pass through this potting
material on each side of the potting material.  The crystal wires are at
the pin # 1 and 24 end of the DIP and the battery is at the pin # 12 and
13 end.  These wires do not necessarily connect to these pins.

The idea is to cut through the potting material, disconnect the positive
internal battery wire and solder a new battery to the wire coming out of
the DIP nearest to pin 13 and the other to pin 12 (ground) of the DIP.

The positive (+) wire is towards pin 13 (but is not connected to it). 
Ground is pin 12 (the external pin on the DIP).

I found a hacksaw blade the ideal tool to slowly cut through the potting
material.  From time to time I would probe in the cut spot with a
voltmeter (gnd to pin 12) to see if I had reached the positive wire.
Even though the battery is near death, mine measured 0.9 volts which is
enough to detect.  Then I continued cutting and scratching until the
wire was exposed.  The rest is easy.  Cut the wire in two and solder the
positive terminal of the new battery to the lower wire (ie the one that
comes out of the DIP).  The wire is not microscopic and relatively easy
to work with once exposed.

A picture would be worth a million words, nay, a -billion- at this
point.  Once you have done one, it would be easy to do many.  I used a
small 3 volt clock battery that had two tabs spot welded on it.  
Works great for me!  Good Luck!

Please send suggestions for this article to
The original idea for this was provided by Michael Coughlin at MIT.

C)  Where does the name "VME" come from?
In case you are new to this newsgroup...
an article written by John Black:

                           What meaneth VME?
In 1981, when Motorola agreed to allow Mostek and Signetics to second
source the MC68000 microprocessor chip, the three companies agreed to
meet and discuss the possibility of supporting a common backplane bus. 
At that time Motorola had already developed a 68000-based backplane bus,
which they called VERSAbus.  Since I had written a large portion of the
VERSAbus specification, I was the Motorola technical representative at
that meeting.

Motorola proposed that the three companies jointly support the VERSAbus
backplane.  However, both Mostek and Signetics rejected that proposal,
saying that the VERSAbus board size was much too large.  In response to
that objection, Motorola proposed that the (much smaller) Eurocard board
size be used.  A backplane could then be designed with the VERSAbus
electrical specifications and the Eurocard mechanical specifications. 
Motorola suggested that new board products (based on this new backplane)
be called VERSAmodule Eurocards, which could be abbreviated "VME".

Both Mostek and Signetics were satisfied with the choice of the Eurocard
mechanical standard, but they objected to the "VERSAmodule Eurocard"
name, since Motorola had already trademarked the name "VERSAmodule".

Eventually this difficulty was overcome when the three companies agreed
that the name VMEbus would be placed in the public domain, and that if
anybody asked what VME meant; they would say....

       "VME?...Oh, it doesn't stand for anything in particular".

                     Now you know the awful truth.

                              John Black
                        VMEbus Systems Magazine
                            Tempe, Arizona

(reprinted here with John's permission)


The purpose of this section is to profile some of the products of
various manufacturers to give an idea of what is available to the
designer and the state of the market.  This section will be rotated and
previous sections will be archived.

Next month (hopefully) will be Pivotal Graphics.


Most Friendly Contributors:

       Andy Fraser         Ontario
       John Black          Arizona
       Michael Coughlin    Massachusets  (sold me my first VME board!)
       Gerry Belanger      Connecticut
       Bosco Chan          Ontario
       Michael Bodine      Ilinois


   and more to come.....

Please send all comments to:

Robert Boys
2055 Gateway Place
San Jose, California, 95110    or

Thank you

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