Datasheet

 2009-2012 Microchip Technology Inc. DS70594D-page 133
dsPIC33FJXXXMCX06A/X08A/X10A
8.0 DIRECT MEMORY ACCESS
(DMA)
Direct Memory Access (DMA) is a very efficient
mechanism of copying data between peripheral SFRs
(e.g., the UART Receive register and Input Capture 1
buffer) and buffers or variables stored in RAM, with
minimal CPU intervention. The DMA controller can
automatically copy entire blocks of data without
requiring the user software to read or write the
peripheral Special Function Registers (SFRs) every
time a peripheral interrupt occurs. The DMA controller
uses a dedicated bus for data transfers, and therefore,
does not steal cycles from the code execution flow of
the CPU. To exploit the DMA capability, the
corresponding user buffers or variables must be
located in DMA RAM.
The dsPIC33FJXXXMCX06A/X08A/X10A peripherals
that can utilize DMA are listed in Tabl e 8- 1 along with
their associated Interrupt Request (IRQ) numbers.
TABLE 8-1: PERIPHERALS WITH DMA
SUPPORT
The DMA controller features eight identical data
transfer channels. Each channel has its own set of
control and status registers. Each DMA channel can be
configured to copy data, either from buffers stored in
dual port DMA RAM to peripheral SFRs, or from
peripheral SFRs to buffers in DMA RAM.
The DMA controller supports the following features:
• Word or byte-sized data transfers.
• Transfers from peripheral to DMA RAM or DMA
RAM to peripheral.
• Indirect Addressing of DMA RAM locations with or
without automatic post-increment.
• Peripheral Indirect Addressing – In some
peripherals, the DMA RAM read/write addresses
may be partially derived from the peripheral.
• One-Shot Block Transfers – Terminating DMA
transfer after one block transfer.
• Continuous Block Transfers – Reloading DMA
RAM buffer start address after every block
transfer is complete.
• Ping-Pong Mode – Switching between two DMA
RAM start addresses between successive block
transfers, thereby filling two buffers alternately.
• Automatic or manual initiation of block transfers.
• Each channel can select from 20 possible
sources of data sources or destinations.
For each DMA channel, a DMA interrupt request is
generated when a block transfer is complete.
Alternatively, an interrupt can be generated when half of
the block has been filled.
Note 1: This data sheet summarizes the features
of the
dsPIC33FJXXXMCX06A/X08A/X10A
family of devices. However, it is not
intended to be a comprehensive refer-
ence source. To complement the infor-
mation in this data sheet, refer to Section
22. “Direct Memory Access (DMA)”
(DS70182) in the “dsPIC33F/PIC24H
Family Reference Manual”, which is
available from the Microchip web site
(www.microchip.com).
2: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.
Peripheral IRQ Number
INT0 0
Input Capture 1 1
Input Capture 2 5
Output Compare 1 2
Output Compare 2 6
Timer2 7
Timer3 8
SPI1 10
SPI2 33
UART1 Reception 11
UART1 Transmission 12
UART2 Reception 30
UART2 Transmission 31
ADC1 13
ADC2 21
ECAN1 Reception 34
ECAN1 Transmission 70
ECAN2 Reception 55
ECAN2 Transmission 71