> 3) My Pro380 cable (bcc03-o6) won't work with RB, what's wrong ??
>    The pin orders seemed to be quite the same.

The Rainbow uses a BCC17 cable with the VR241 color monitor, NOT the BCC03 cable
used by the Professional, DECmate and VT241 terminal. -- Here in the United
States, Digital Equipment Corporation (DEC) is selling the BCC17-6 cable for $56
US.

BCC03 and BCC17 cables
======================
The following data was extracted from the PDP-11 Systems And Options Catalog,
October - December 1984 (DEC part number ED-26049-41), page 4-19.

The cables consist of three 30 AWG coax cables and four 20-AWG stranded
conductors with a 38 AWG tinned copper braid shield.  The connectors are:

    P1 = 15 position D subminiature
    P2 = keyboard plug
    P3 = "B" BNC
    P4 = "G" BNC
    P5 = "R" BNC
    
The wiring is:

    P1-1  -- P3 coax shield
    P1-2  -- P4 coax shield
    P1-3  -- P5 coax shield
    P1-4  -- --------------
    P1-5  -- P1-13 jumper
    P1-6  -- P2-3 conductor
    P1-7  -- --------------
    P1-8  -- P2-2 conductor
    P1-9  -- P3 coax center
    P1-10 -- P4 coax center in BCC03 only -- nothing in BCC17
    P1-11 -- P5 coax center
    P1-12 -- P4 coax center in BCC17 only -- nothing in BCC03
    P1-13 -- P1-5 jumper
    P1-14 -- P2-1 conductor
    P1-15 -- P2-4 conductor


Rainbow keyboard / monitor connector (J3)
=========================================
The following pin assignments for the Rainbow keyboard/monitor connector were
extracted from "PC100 Mother Board" skematic (DEC drawing size D, code CS,
number 5415486-0-1, revision E) which is included in the "PC100 Field Maintenace
Print Set (DEC part number MP-01491-00).   The assignments are also listed in
the Rainbow 100 Technical Manual (DEC part number EK-PC100-TM-001), table 3-6 on
page 3-22 except that table shows the keyboard data flowing in directions
opposite that shown on the skematic and listed below.

The BCC02 monochrome cable wiring was obtained by inspecting that cable.  BCC03
and BCC17 cable wiring was from the source listed above.

                                    BCC02  BCC03  BCC17  Possible
    Rainbow                    Pin  Mono   Color  Color  Dual Monitor
    =======                    ===  =====  =====  =====  ============
    Red shield ground -------  1    -----    X      X       Color
    Green shield ground -----  2    -----    X      X       Color
    Blue shield ground ------  3    -----    X      X       Color
    Mono shield ground ------  4      X    -----  -----   Monochrome
    Ground ------------------  5      X    jumper jumper  Monochrome
    Ground ------------------  6      X      X      X      Keyboard
    +12 volts ---------------  7      X    -----  -----   Monochrome
    +12 volts ---------------  8      X      X      X      Keyboard
    Blue video --------------  9    -----    X      X       Color
    Green video -------------  10   -----    X    -----     Color
    Red video ---------------  11   -----    X      X       Color
    Mono video --------------  12     X    -----    X     Monochrome
    -- not used -------------  13   -----  jumper jumper    -----
    Data from keyboard to CPU  14     X      X      X      Keyboard
    Data from CPU to keyboard  15     X      X      X      Keyboard


Conclusion
==========
Comparison of the above data suggests that when the graphics board is in a
Rainbow, the BCC03 cable should route the color graphics signals to the VR241
monitor.  However, the monochrome signal generated on the Rainbow's motherboard
will NOT be capable of being displayed with the BCC03 cable.

As indicated in the "Rainbow Color/Graphics Option Programmer's Reference
Guide" (DEC part number AA-AE36A-TV), the Rainbow can support three different
monitor configurations: (1) monochrome monitor only, (2) color monitor only, and
(3) both monochrome and color monitors.  Each of the single monitor
configurations presents a problem, that is how to get graphics video data to the
monochrome monitor, and how to get motherboard video data to the color monitor.
DEC solved these problems with a electronic switch on the motherboard.  That
switch is controlled by bit 2 of port 0A hexidecimal.  Setting that bit to 0
places motherboard video data on pin 12 of the BCC02 / BCC17 cable.  In
contrast, setting the bit to 1 puts graphics option "green" data on that pin.

To my knowledge, DEC never sold a cable to support the Rainbow's dual monitor
configuration.  However, some people have built such a cable.

(Note: The above data suggests a Professional or DECmate, when equipped with
its graphics option and an appropriate cable, may also be capable of supporting
a dual monitor configuration.)


Carl C. Hoff
choff@cs.wrigth.edu