SAM9G20 Atmel Corporation, SAM9G20 Datasheet - Page 400
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SAM9G20
Manufacturer Part Number
SAM9G20
Description
Manufacturer
Atmel Corporation
Datasheets
1.SAM9261.pdf
(248 pages)
2.SAM9261.pdf
(1274 pages)
3.SAM9261.pdf
(43 pages)
4.SAM9G20.pdf
(42 pages)
5.SAM9G20.pdf
(832 pages)
Specifications of SAM9G20
Flash (kbytes)
0 Kbytes
Pin Count
217
Max. Operating Frequency
400 MHz
Cpu
ARM926
Hardware Qtouch Acquisition
No
Max I/o Pins
96
Ext Interrupts
96
Usb Transceiver
3
Usb Speed
Full Speed
Usb Interface
Host, Device
Spi
2
Twi (i2c)
1
Uart
7
Ssc
1
Ethernet
1
Sd / Emmc
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
Yes
Adc Channels
4
Adc Resolution (bits)
10
Adc Speed (ksps)
95
Resistive Touch Screen
No
Temp. Sensor
No
Crypto Engine
No
Sram (kbytes)
32
Self Program Memory
NO
External Bus Interface
1
Dram Memory
sdram
Nand Interface
Yes
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8/3.3
Operating Voltage (vcc)
0.9 to 1.1
Fpu
No
Mpu / Mmu
No/Yes
Timers
6
Output Compare Channels
6
Input Capture Channels
6
32khz Rtc
Yes
Calibrated Rc Oscillator
No
- SAM9261 PDF datasheet
- SAM9261 PDF datasheet #2
- SAM9261 PDF datasheet #3
- SAM9G20 PDF datasheet #4
- SAM9G20 PDF datasheet #5
- Current page: 400 of 832
- Download datasheet (13Mb)
30.6.3.6
30.6.3.7
400
AT91SAM9G20
Peripheral Chip Select Decoding
Peripheral Deselection
Fixed Peripheral Select is activated by writing the PS bit to zero in SPI_MR (Mode Register). In
this case, the current peripheral is defined by the PCS field in SPI_MR and the PCS field in the
SPI_TDR has no effect.
Variable Peripheral Select is activated by setting PS bit to one. The PCS field in SPI_TDR is
used to select the current peripheral. This means that the peripheral selection can be defined for
each new data.
The Fixed Peripheral Selection allows buffer transfers with a single peripheral. Using the PDC is
an optimal means, as the size of the data transfer between the memory and the SPI is either 8
bits or 16 bits. However, changing the peripheral selection requires the Mode Register to be
reprogrammed.
The Variable Peripheral Selection allows buffer transfers with multiple peripherals without repro-
gramming the Mode Register. Data written in SPI_TDR is 32 bits wide and defines the real data
to be transmitted and the peripheral it is destined to. Using the PDC in this mode requires 32-bit
wide buffers, with the data in the LSBs and the PCS and LASTXFER fields in the MSBs, how-
ever the SPI still controls the number of bits (8 to16) to be transferred through MISO and MOSI
lines with the chip select configuration registers. This is not the optimal means in term of mem-
ory size for the buffers, but it provides a very effective means to exchange data with several
peripherals without any intervention of the processor.
The user can program the SPI to operate with up to 15 peripherals by decoding the four Chip
Select lines, NPCS0 to NPCS3 with an external logic. This can be enabled by writing the PCS-
DEC bit at 1 in the Mode Register (SPI_MR).
When operating without decoding, the SPI makes sure that in any case only one chip select line
is activated, i.e. driven low at a time. If two bits are defined low in a PCS field, only the lowest
numbered chip select is driven low.
When operating with decoding, the SPI directly outputs the value defined by the PCS field of
either the Mode Register or the Transmit Data Register (depending on PS).
As the SPI sets a default value of 0xF on the chip select lines (i.e. all chip select lines at 1) when
not processing any transfer, only 15 peripherals can be decoded.
The SPI has only four Chip Select Registers, not 15. As a result, when decoding is activated,
each chip select defines the characteristics of up to four peripherals. As an example, SPI_CRS0
defines the characteristics of the externally decoded peripherals 0 to 3, corresponding to the
PCS values 0x0 to 0x3. Thus, the user has to make sure to connect compatible peripherals on
the decoded chip select lines 0 to 3, 4 to 7, 8 to 11 and 12 to 14.
When operating normally, as soon as the transfer of the last data written in SPI_TDR is com-
pleted, the NPCS lines all rise. This might lead to runtime error if the processor is too long in
responding to an interrupt, and thus might lead to difficulties for interfacing with some serial
peripherals requiring the chip select line to remain active during a full set of transfers.
To facilitate interfacing with such devices, the Chip Select Register can be programmed 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 peripheral is required.
• Variable Peripheral Select: Data can be exchanged with more than one peripheral
6384E–ATARM–05-Feb-10
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