MB86330 Fujitsu Media Devices Limited, MB86330 Datasheet - Page 25

• Manufacturer Part Number: MB86330
• Description: 16-bit Fixed-point DSP
• Manufacturer: Fujitsu Media Devices Limited

1. Data Format
Integral type and fixed-point data can be handled regardless of whether the data is signed or unsigned. For
signed data, the most significant bit indicates a sign. A number of 1 indicates negative data, which is expressed
by 2’s complement. The decimal point for fixed-point type data is located between the sign bit (bit 14) and its
right bit (bit 15). When the accumulator value resulting from execution of a multiplication instruction is transferred
to a 16-bit length register or memory, the decimal point is returned to the original position (between bits 14 and 15).
• Fixed-point type, signed data
• Fixed-point type, unsigned data
• Integral-type, signed data
• Integral-type, unsigned data
Since a value is handled in 2’s complement format for addition and subtraction, no distinction is made in the
result of an operation by the above four data format. Since, for multiplication, the result of an operation varies
with whether data is signed or unsigned, three combinations of “signed data x signed data,” “signed data
unsigned data,” and “unsigned data
For the fixed-point type and the integral type, the result of multiplication varies with the decimal point position.
When fixed-point type data is multiplied, the result of the operation is stored into the accumulator with one bit
shifted to the left in comparison with integral type data. The “ITG” bit in the status register is used to switch
between the fixed-point type and the integral type. With this bit set at 0, an operation is executed in the fixed-
point type format.
BASIC CONFIGURATION OF THE DATA OPERATION SECTION
Sign
Sign
15
15
15
15
S
S
Decimal point
14
14
14
14
Decimal point
13
13
13
13
12
12
12
12
11
11
11
11
unsigned data” exist for multiplication instructions.
10
10
10
10
Decimal part (2’s complement)
Integral part (2’s complement)
9
9
9
9
Integral part
Decimal part
8
8
8
8
7
7
7
7
6
6
6
6
5
5
5
5
4
4
4
4
3
3
3
3
2
2
2
2
1
1
1
1
0
0
0
0
www.DataSheet4U.com
MB86330
bit
bit
bit
bit
25