Bulletin number:  4
Products affected:  B004
Description:  B004 Upgrade to T800S
Component:  T800S
Date:  Tue May 26 00:00:00 GMT 1988

Here is a slighly more detailed description of how to modify in IMSBOO4-4
so that it may take up to 20 MHz processor.

1.  Take standard IMSBOO4-4 and remove transputer to prevent damage.

2.  Unsolder 25 MHz clock osc. and place a 5 MHz clock osc. in its place.

3.  Cut track on underside of BOO4 from pin B1>C2 of the transputer.
    This changes the pin Disable PLL from HIGH to UNCONNECTED.
    NOTE:  For a T414 this works OK as T414's have pull-down resistor on-
           chip, however, this is not the case for the T800, therefore
           it is also necessary to tie B1>C1, thus holding DisablePLL LOW.
 
If B1 is not tied to C1, a T800-22 will result from placing a T800 in the
transputer socket.  At room temperature, I found this worked o.k. (100ns
DRAMS).

4.  Cut track on upperside of BOO4 from pin 11   on the IMSCOO3 to the blob
    on  the PCB.  This track is under the COO3, which must therefore be
    removed first.  The COO3 has pull-downs and so pin 11 does not need
    grounding.  This mod enables the PLL on the COO3.

AT THIS STAGE IT IS POSSIBLE TO USE T414-15, T414-20, T800-20 transputers
all with a 5 cycle memory interface.

5.  In order to get to a 3 cycle memory interface all memory DRAMS must
    be swapped out.  I used IMS280x-60 parts (60ns), but I am told 70's
    and 80's may work also.

6.  Lastly it is required to modify the memory configuration so that it
    uses the INTERNAL configuration associated with AD4, instead of an
    EXTERNAL configuration.  This is achieved by cutting the track on the
    upperside of the BOO4 between pin 19 of the F373, and pin C8 (Mem Conf.)
    of the transputer.  Once this is done C8 must be connected to H8 (AD4).

7.  Now plug in the transputer of your choice and the COO3 and zoom away.