TMP86FS23UG datasheet(194/252 Pages) TOSHIBA

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Page 182

17. Multiply-Accumulate (MAC) Unit

17.6 Status Flags

TMP86FS23UG

causes the result and addend registers to be cleared. After calculation is completed, the contents of the result

changed, the result of the previous multiply-accumulate operation is used as an addend for the next calculation.

Note 1: Be sure to write to the addend register when calculation is not being performed (CALC = “0”).

Note 2: Writing to the addend register changes the contents of the result register. Thus, read from the result register

before writing to the addend register.

17.5.4 Signed Multiply-Accumulate Mode

Setting the MACCR<CMOD> field in the command register to “011B” places the MAC unit in signed mul-

tiply-accumulate mode. In this mode, bit 15 in the multiplier and multiplicand register is each treated as the

sign bit.

Calculation is started automatically by writing a multiplier to the multiplier register (MPLDRH, MPLDRL)

and then writing a multiplicand to the lower byte (MPCDRL) and upper byte (MPCDRH) of the multiplicand

RCALDR1). The sign of the result varies as shown in Table 17-4. As in the case of unsigned multiply-accumu-

late mode, any addend can be written to the addend register when calculation is not being performed.

Note: In signed multiply-accumulate mode, bit 31 in the addend register is treated as the sign bit.

17.5.5 Valid Numerical Ranges

Table 17-5 shows the numerical range that can be handled in each arithmetic mode.

17.6 Status Flags

The status register MACSR contains the following five flags. OVRF, CARF, SIGN, and ZERF are programmed

when calculation is completed, and these flags are not affected by a read from the status register.

1. Operation status flag (CALC)

2. Overflow flag (OVRF)

3. Carry flag (CARF)

4. Sign flag (SIGN)

5. Zero flag (ZERF)

Table 17-4 Signs Used in Sgined Multiply-Accumulate Mode

Sign of Product

Sign of Addend

Sign (bit 31) of Calculation Result

When OVRF = “0”

When OVRF = “1”

“1” when sum < 0

“0” when sum

≥ 0

–

“1” when sum < 0

“0” when sum

≥ 0

–

Table 17-5 Valid Numerical Ranges in Decimal (with hexadecimal shown in brackets)

Mode

Multiplier/Multiplicand

Addend

Sum

Unsigned multiply

0 to 65535

(0000H to FFFFH)

–

0 to 4294836225

(00000000H to FFFE0001H)

Signed multiply

-32768 to 32767

(8000H to 7FFFH)

–

-1073709056 to 1073741824

(C0008000H to 40000000H)

Unsigned multiply-

accumulate

0 to 65535

(0000H to FFFFH)

0 to 4294967295

(00000000H to FFFFFFFFH)

0 to 4294967295

(00000000H to FFFFFFFFH)

Signed multiply-

accumulate

-32768 to 32767

(8000H to 7FFFH)

-2147483648 to 2147483647

(80000000H to 7FFFFFFFH)

-2147483648 to 2147483647

(80000000H~7FFFFFFFH)

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