Texas Instruments 990 Operation Manual page 257

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945255-9701
APPENDIXF
MEMORY AND PROM MAPPING
Bit strings are fetched from and stored into the 990 memory and PROM under control of
memory and PROM mapping parameters. These parameters are used to evaluate a mathematical
expression w~ch determines the beginning bit address of a bit string.
The mapping parameters are:
IMl ,1M 2 ,1M3
IR
1
,IR2 , IR 3
The increment values associated with
each term of the polynomial (in
bits)
MMl ,MM2 ,MM3 The maximum multiplier for the
MRl ,MR2 ,MR3 increment for each term of the
polynomial
DMl ,DM 2 ,DM3 The initial displacement associated
DR! ,DR 2 ,DR3 with each term of the polynomial
(in bits)
BMA,BCA
RWW
Beginning memory (byte) address and beginning chip (physical word) address
PROM/ROM physical word width
Note that the condition
3
IIMM·=
. 1
1
1=
3
IIMRi must be met, namely
i=I
that the algorithm will map an identical number of bit strings in memory as it will in
PROM/ROM.
3
3
Let n = IIMMi -1
==
IIMRi -1.
i=1
Let K = 0,1,2 ... ,n
Then compute
i=1
CM l
=
k
modulo MMI
CM
2
=
int
(M~l
)
CM 3
=
int
(MMl~
MM 2 )
Then beginning memory bit address of string
3
BMBA = 8 . BMA + L (DM i + CM
i . IM i )
i= 1
F-l
CRl
=
k modulo MRl
CR2
=
int (M\.l )
. . K
CR
=
mt (MR!· MR2 )
Digital Systems Division