Intel 2920 Design Handbook page 30

THE 2920 SIGNAL PROCESSOR
'A" ADR "B" ADR
RAM
STORAGE
40
x
25
CONSTANTS
DAR
SHF ALU
A
CY OUT
CND _ _ _ _ _
- - J
TEST BIT
- - - - - - - - - 1
Figure
3-3.
Arithmetic Unit and Memory
Data within this structure are processed using 25-bit
two's complement arithmetic. It is most convenient to
consider an imaginary binary point just to the right of
the MSB (Most Significant Bit) which is the sign bit.
Thus the normal range of any variable x is considered to
be
-1.0<x<1.0
and the smallest resolvable change, d, in any variable is
given by
d = 2-
24
=5.96*10- 8
Each of the elements making up this portion of the 2920
receives command or address information from the
EPROM. The storage array receives two 6-bit address
fields, the scaler receives a 4-bit control field, and the
ALU receives a 3-bit control field.
The Storage Array and the Constant Array-The
storage array consists of a random access memory, with
two ports, organized as 40 words of 25 bits each. Each
port is independently controlled from the EPROM by a
6-bit control field.
The two ports are called "A" and "B." The A port is
read-only. Data read from it are passed, through the
scaler, to one input of the ALU, as the source operand.
The B port passes data to the second ALU input, and
receives the ALU results, as the destination operand.
The constant array consists of 16 "pseudo-locations" in
the RAM address field. These constants are accessed
only from the A port, i.e., only as a source operand.
3-5
The least significant four bits of the "address" are
directly translated to the high-order four bits of the data
field, with the remaining data bits equivalent to zeroes.
Therefore, each unsealed constant is a multiple of one-
eighth, from -8/8, -718,00', up to +6/8, +7/8. A
much wider range of constants is actually available,
because the selected constant passes through the scaler,
and can thus be modified as explained below. Figure 3-4
shows the "address" mapping for constants. Table 3-2
shows the assembly language mnemonics for the con-
stants and the corresponding values.
~
A" PORT DATA WORD
1 1 II!
!
lAS
+.
- 1 1
A,
I
A,
I
A,
I
Ao
1-
A"ADDRESS
Figure 3-4. Address Mapping for Constants
Table
3-2.
Constant Codes
Constant Unscaled Constant Unscaled
Mnemonic Value Mnemonic Value
KPO 0 0.000
KMI - .125 1.111
KPI +.125 0.001 KM2 - .250 1.110
KP2 +.250 0.010 KM3 - .375 1.101
KP3 +.375 0.011 KM4 - .500 1.100
KP4 +.500 0.100 KM5
- .625 1.011
KP5 +.625 0.101 KM6 - .750 1.010
KP6 +.750 0.110 KM7
- .875 1.001
KP7 +.875 0.111 KM8
-1.0 1.000