PIC18F45J50-I/SOSQTP 查看數據表（PDF） - Microchip Technology

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PIC18F45J50-I/SOSQTP

28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology

Microchip Technology 

PIC18F46J50 FAMILY

EXAMPLE 19-2: 512-BYTE SPI MASTER MODE Init AND TRANSFER (CONTINUED)

;

;DestBuf

;

;SrcBuf

;

udata

res

res

0x500

0x200

0x200

PrepareTransfer:

movlw

HIGH(DestBuf)

movwf

RXADDRH

movlw

LOW(DestBuf)

movwf

RXADDRL

movlw

movwf

movlw

movwf

HIGH(SrcBuf)

TXADDRH

LOW(SrcBuf)

TXADDRL

movlw

movwf

movlw

movwf

0x01

DMABCH

0xFF

DMABCL

BeginXfer:

bsf

DMACON1, DMAEN

;Execute whatever

;Somewhere else in our project, lets assume we have

;allocated some RAM for use as SPI receive and

;transmit buffers.

;Let’s reserve 0x500-0x6FF for use as our SPI

;receive data buffer in this example

;Lets reserve 0x700-0x8FF for use as our SPI

;transmit data buffer in this example

;Get high byte of DestBuf address (0x05)

;Load upper four bits of the RXADDR register

;Get low byte of the DestBuf address (0x00)

;Load lower eight bits of the RXADDR register

;Get high byte of SrcBuf address (0x07)

;Load upper four bits of the TXADDR register

;Get low byte of the SrcBuf address (0x00)

;Load lower eight bits of the TXADDR register

;Lets move 0x200 (512) bytes in one DMA xfer

;Load the upper two bits of DMABC register

;Actual bytes transferred is (DMABC + 1), so

;we load 0x01FF into DMABC to xfer 0x200 bytes

;The SPI DMA module will now begin transferring

;the data taken from SrcBuf, and will store

;received bytes into DestBuf.

;CPU is now free to do whatever it wants to

;and the DMA operation will continue without

;intervention, until it completes.

;When the transfer is complete, the SSP2IF flag in

;the PIR3 register will become set, and the DMAEN bit

;is automatically cleared by the hardware.

;The DestBuf (0x500-0x7FF) will contain the received

;data. To start another transfer, firmware will need

;to reinitialize RXADDR, TXADDR, DMABC and then

;set the DMAEN bit.

 2011 Microchip Technology Inc.

DS39931D-page 287

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