AT91SAM9M10-G45-EK Atmel, AT91SAM9M10-G45-EK Datasheet - Page 412

• Manufacturer Part Number: AT91SAM9M10-G45-EK
• Description: KIT EVAL FOR AT91SAMG45/9M10
• Manufacturer: Atmel
• Series: AT91SAM Smart ARMr
• Type: MCUr

Specifications of AT91SAM9M10-G45-EK

• Contents: Board, Cables, Power Supply
• Processor To Be Evaluated: AT91SAM9M10
• Processor Series: AT91SAM9
• Data Bus Width: 32 bit
• Interface Type: RS-232, Ethernet, USB, JTAG
• Operating Supply Voltage: 5 V
• Silicon Manufacturer: Atmel
• Core Architecture: AVR
• Kit Contents: Board
• Features: Two High Speed USB Hosts, LCD TFT Display
• Svhc: No SVHC (15-Dec-2010)
• Mcu Supported Families: AT91SAM9M10,
• Rohs Compliant: Yes
• For Use With/related Products: AT91SAM9M10
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

28.7.3.10
28.7.3.11
28.7.3.12
412
AT91SAM9M10
Peripheral Deselection without PDCDMAC
Peripheral Deselection with PDC
Peripheral Deselection with DMAC
During a transfer of more than one data on a Chip Select without the PDCDMAC, the SPI_TDR
is loaded by the processor, the flag TDRE rises as soon as the content of the SPI_TDR is trans-
ferred into the internal shift register. When this flag is detected high, the SPI_TDR can be
reloaded. If this reload by the processor occurs before the end of the current transfer and if the
next transfer is performed on the same chip select as the current transfer, the Chip Select is not
de-asserted between the two transfers. But depending on the application software handling the
SPI status register flags (by interrupt or polling method) or servicing other interrupts or other
tasks, the processor may not reload the SPI_TDR in time to keep the chip select active (low). A
null Delay Between Consecutive Transfer (DLYBCT) value in the SPI_CSR register, will give
even less time for the processor to reload the SPI_TDR. With some SPI slave peripherals,
requiring the chip select line to remain active (low) during a full set of transfers might lead to
communication errors.
To facilitate interfacing with such devices, the Chip Select Register [CSR0...CSR3] can be pro-
grammed with the CSAAT bit (Chip Select Active After Transfer) at 1. This allows the chip select
lines to remain in their current state (low = active) until transfer to another chip select is required.
Even if the SPI_TDR is not reloaded the chip select will remain active. To have the chip select
line to raise at the end of the transfer the Last transfer Bit (LASTXFER) in the SPI_MR register
must be set at 1 before writing the last data to transmit into the SPI_TDR.
When the Peripheral DMA Controller is used, the chip select line will remain low during the
whole transfer since the TDRE flag is managed by the PDC itself. The reloading of the SPI_TDR
by the PDC is done as soon as TDRE flag is set to one. In this case the use of CSAAT bit might
not be needed. However, it may happen that when other PDC channels connected to other
peripherals are in use as well, the SPI PDC might be delayed by another (PDC with a higher pri-
ority on the bus). Having PDC buffers in slower memories like flash memory or SDRAM
compared to fast internal SRAM, may lengthen the reload time of the SPI_TDR by the PDC as
well. This means that the SPI_TDR might not be reloaded in time to keep the chip select line
low. In this case the chip select line may toggle between data transfer and according to some
SPI Slave devices, the communication might get lost. The use of the CSAAT bit might be
needed.
When the Direct Memory Access Controller is used, the chip select line will remain low during
the whole transfer since the TDRE flag is managed by the DMAC itself. The reloading of the
SPI_TDR by the DMAC is done as soon as TDRE flag is set to one. In this case the use of
CSAAT bit might not be needed. However, it may happen that when other DMAC channels con-
nected to other peripherals are in use as well, the SPI DMAC might be delayed by another
(DMAC with a higher priority on the bus). Having DMAC buffers in slower memories like flash
memory or SDRAM compared to fast internal SRAM, may lengthen the reload time of the
SPI_TDR by the DMAC as well. This means that the SPI_TDR might not be reloaded in time to
keep the chip select line low. In this case the chip select line may toggle between data transfer
and according to some SPI Slave devices, the communication might get lost. The use of the
CSAAT bit might be needed.
Figure 28-12
shows different peripheral deselction cases and the effect of the CSAAT bit.
6355B–ATARM–21-Jun-10