PIC24EP64MC204-E/PT Microchip Technology, PIC24EP64MC204-E/PT Datasheet - Page 112

• Manufacturer Part Number: PIC24EP64MC204-E/PT
• Description: 16 Bit MCU, 64KB Flash, 8KB RAM, 60 MHz, 44 Pin, MCPWM,QEI, 3 OpAmp, 4 Comp, PTG
• Manufacturer: Microchip Technology

dsPIC33EPXXXGP50X, dsPIC33EPXXXMC20X/50X, AND PIC24EPXXXGP/MC20X
4.6.3
Modulo Addressing can be applied to the Effective
Address (EA) calculation associated with any W
register. Address boundaries check for addresses
equal to:
• The upper boundary addresses for incrementing
• The lower boundary addresses for decrementing
It is important to realize that the address boundaries
check for addresses less than or greater than the upper
(for incrementing buffers) and lower (for decrementing
buffers) boundary addresses (not just equal to).
Address changes can, therefore, jump beyond
boundaries and still be adjusted correctly.
4.7
Bit-Reversed Addressing mode is intended to simplify
data reordering for radix-2 FFT algorithms. It is
supported by the X AGU for data writes only.
The modifier, which can be a constant value or register
contents, is regarded as having its bit order reversed.
The address source and destination are kept in normal
order. Thus, the only operand requiring reversal is the
modifier.
DS70657F-page 112
buffers
buffers
Note:
Bit-Reversed Addressing
(dsPIC33EPXXXMC20X/50X and
dsPIC33EPXXXGP50X Devices
Only)
MODULO ADDRESSING
APPLICABILITY
The modulo corrected effective address is
written back to the register only when Pre-
Modify or Post-Modify Addressing mode is
used to compute the effective address.
When an address offset (such as [W7 +
W2]) is used, Modulo Address correction
is performed but the contents of the
register remain unchanged.
4.7.1
Bit-Reversed Addressing mode is enabled in any of
these situations:
• BWM bits (W register selection) in the MODCON
• The BREN bit is set in the XBREV register
• The addressing mode used is Register Indirect
If the length of a bit-reversed buffer is M = 2
the last ‘N’ bits of the data buffer start address must
be zeros.
XB<14:0> is the Bit-Reversed Address modifier, or
‘pivot point,’ which is typically a constant. In the case of
an FFT computation, its value is equal to half of the FFT
data buffer size.
When enabled, Bit-Reversed Addressing is executed
only for Register Indirect with Pre-Increment or Post-
Increment Addressing and word-sized data writes. It
does not function for any other addressing mode or for
byte-sized data, and normal addresses are generated
instead. When Bit-Reversed Addressing is active, the
W Address Pointer is always added to the address
modifier (XB), and the offset associated with the
Register Indirect Addressing mode is ignored. In
addition, as word-sized data is a requirement, the LSb
of the EA is ignored (and always clear).
If Bit-Reversed Addressing has already been enabled
by setting the BREN (XBREV<15>) bit, a write to the
XBREV register should not be immediately followed by
an indirect read operation using the W register that has
been designated as the bit-reversed pointer.
register are any value other than ‘1111’ (the stack
cannot be accessed using Bit-Reversed
Addressing)
with Pre-Increment or Post-Increment
Note:
Note:
BIT-REVERSED ADDRESSING
IMPLEMENTATION
All bit-reversed EA calculations assume
word-sized data (LSb of every EA is
always clear). The XB value is scaled
accordingly to generate compatible (byte)
addresses.
Modulo
addressing can be enabled simultaneously
using the same W register, but bit-reversed
addressing operation will always take
precedence for data writes when enabled.
 2011-2012 Microchip Technology Inc.
addressing
and
bit-reversed
N
bytes,