MA330026 Microchip Technology, MA330026 Datasheet - Page 35

• Manufacturer Part Number: MA330026
• Description: Daughter Cards & OEM Boards dsPIC33FJ16MC102 Plug-In Module
• Manufacturer: Microchip Technology

Specifications of MA330026

• Rohs: yes
• Product: Plug-In Modules
• Core: PIC
• Data Bus Width: 16 bit
• Description/function: dsPIC33F MC 28 Pin QFN to 100 Pin Plug-in-Module
• Interface Type: I2C, SPI, UART
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Operating Supply Voltage: 3 V to 3.6 V
• For Use With: DM330021, DM330022, DM330023

3.6.3.1
The round logic is a combinational block that performs
a conventional (biased) or convergent (unbiased)
round function during an accumulator write (store). The
Round mode is determined by the state of the RND bit
in the CORCON register. It generates a 16-bit, 1.15
data value that is passed to the data space write
saturation logic. If rounding is not indicated by the
instruction, a truncated 1.15 data value is stored and
the least significant word (lsw) is simply discarded.
Conventional rounding will zero-extend bit 15 of the
accumulator and will add it to the ACCxH word (bits 16
through 31 of the accumulator).
• If the ACCxL word (bits 0 through 15 of the accu-
• If ACCxL is between 0x0000 and 0x7FFF, ACCxH
A consequence of this algorithm is that over a succes-
sion of random rounding operations, the value tends to
be biased slightly positive.
Convergent (or unbiased) rounding operates in the
same manner as conventional rounding, except when
ACCxL equals 0x8000. In this case, the Least
Significant bit (LSb), bit 16 of the accumulator, of
ACCxH is examined:
• If it is ‘1’, ACCxH is incremented.
• If it is ‘0’, ACCxH is not modified.
Assuming that bit 16 is effectively random in nature,
this scheme removes any rounding bias that may
accumulate.
The SAC and SAC.R instructions store either a
truncated (SAC), or rounded (SAC.R) version of the
contents of the target accumulator to data memory via
the
Section 3.6.3.2 “Data Space Write
the MAC class of instructions, the accumulator write-
back operation functions in the same manner,
addressing combined MCU (X and Y) data space
though the X bus. For this class of instructions, the data
is always subject to rounding.
© 2011 Microchip Technology Inc.
mulator) is between 0x8000 and 0xFFFF (0x8000
included), ACCxH is incremented.
is left unchanged.
dsPIC33FJ16GP101/102 AND dsPIC33FJ16MC101/102
X
bus,
Round Logic
subject
to
data
Saturation”). For
saturation
(see
Preliminary
3.6.3.2
In addition to adder/subtracter saturation, writes to data
space can also be saturated, but without affecting the
contents of the source accumulator. The data space
write saturation logic block accepts a 16-bit, 1.15
fractional value from the round logic block as its input,
together with overflow status from the original source
(accumulator) and the 16-bit round adder. These inputs
are combined and used to select the appropriate 1.15
fractional value as output to write to data space
memory.
If the SATDW bit in the CORCON register is set, data
(after rounding or truncation) is tested for overflow and
adjusted accordingly:
• For input data greater than 0x007FFF, data
• For input data less than 0xFF8000, data written to
The MSb of the source (bit 39) is used to determine the
sign of the operand being tested.
If the SATDW bit in the CORCON register is not set, the
input data is always passed through unmodified under
all conditions.
3.6.4
The barrel shifter can perform up to 16-bit arithmetic or
logic right shifts, or up to 16-bit left shifts, in a single
cycle. The source can be either of the two DSP
accumulators or the X bus (to support multi-bit shifts of
register or memory data).
The shifter requires a signed binary value to determine
both the magnitude (number of bits) and direction of the
shift operation. A positive value shifts the operand right.
A negative value shifts the operand left. A value of ‘0’
does not modify the operand.
The barrel shifter is 40 bits wide, thereby obtaining a
40-bit result for DSP shift operations and a 16-bit result
for MCU shift operations. Data from the X bus is
presented to the barrel shifter between bit positions 16
and 31 for right shifts, and between bit positions 0 and
16 for left shifts.
written to memory is forced to the maximum
positive 1.15 value, 0x7FFF.
memory is forced to the maximum negative 1.15
value, 0x8000.
BARREL SHIFTER
Data Space Write Saturation
DS70652C-page 35