14-MAR-89
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                *       CHTCR PROMS                             *
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DESCRIPTION
-----------

    There are three types of PROMS on the CHTCR card. They are:

        1.  First Tier Count 2K x 4
        2.  First Tier Count 4K x 8
        3.  Eta/Phi address mapping

    Each type of PROM requires different programming. This document describes
how the PROM data are generated.


First Tier Count
----------------

    The First Tier Count is the population count of each channel. That is, if n
Trigger Towers of any channel are asserted, the First Tier Count will be n.

    The First Tier  Count is computed in  two stages. The  32 Trigger Towers are
split into three groups, sized 11, 11,  and 10. The (4-bit) partial sums in each
group are computed in the  first stage. The second  stage consists of adding the
three  partial sums  together to  generate  the  (6-bit) First  Tier Count. Both
stages are implemented using PROMs. 

    The first stage  requires three 2K x 4 PROMs.  Each PROM uses as its address
lines the 11  (2**11 = 2048)  Trigger Towers in  a group (in  the case of the 10
Trigger Tower group, an address line is  grounded). The data at each location is
then simply the number of  binary 1's in the 11-bit  address. The maximum number
of 1's in an 11-bit address is 11, hence a 4-bit wide PROM is sufficient. 

    Example: Assume that the lowest 4 Trigger Towers in a group are asserted.
             This would correspond to PROM location 15 (00000001111). There are
             four 1's in this address, hence PROM location 15 should contain the
             value 4.

    The second  stage requires  one 4K x 8  PROM. This PROM  uses as its address
lines the  three  (4-bit)  partial counts  (2**(3*4) =  4096).  The data at each
location is the summation  of the three (4-bit)  partial counts that make up the
address.  The   maximum  result is  32   (corresponding  to  all  Trigger Towers
asserted), therefore a  6-bit wide PROM (if  available) would suffice. We use an
8-bit wide PROM. 

    Example: Assume that the partial counts are 3, 4, and 10. This would
             correspond to PROM location 34A (hex). Since 3+4+10 = 17 (11 hex),
             PROM location 34A (hex) should contain the value 17 (11 hex).

    FORTRAN code has  been written to  generate these  PROMs. The batch files to
provide  to  the  PROM   programmer  are   stored as     CHTCRPROM2048X4.DAT and
CHTCRPROM4096X8.DAT.  If  necessary,  these files  can be  transferred to the PC
using   KERMIT. The   FORTRAN  programs  to  generate  the  PROMs are  stored as
CHTCRPROM2048X4 and CHTCRPROM4096X8. They are in directory
MSUTRGROOT:[000000.PROG_DEV.CHTCR.DEV_DATA] aka CHTCR_DATA.

    The actual PROM data, as well as the batch files mentioned above, are also
stored on the PC floppy disk labelled CHTCR PROMS, and backed up on ROM-PAL #1
and BACKUP OF ROM-PAL #1.

Eta/Phi Address Mapping
-----------------------

    The Eta/Phi mapping  requires two 2K x 8 PROMs,  each logically divided into
32 64-byte sections. The  specifics of these PROMs  are in CHTCR.TXT. The lowest
section of  these PROMs  (address  range 0 to 63)  has been  reserved for a test
pattern.