at91cap7e ATMEL Corporation, at91cap7e Datasheet - Page 325

• Manufacturer Part Number: at91cap7e
• Description: Customizable Microcontroller
• Manufacturer: ATMEL Corporation

28.6.3.3
28.6.3.4
Figure 28-9. Programmable Delays
28.6.3.5
8549A–CAP–10/08
Chip Select 1
Chip Select 2
SPCK
Clock Generation
Transfer Delays
Peripheral Selection
The SPI Baud rate clock is generated by dividing the Master Clock (MCK) or the Master Clock
divided by 32, by a value between 1 and 255. The selection between Master Clock or Master
Clock divided by 32 is done by the FDIV value set in the Mode Register
This allows a maximum operating baud rate at up to Master Clock and a minimum operating
baud rate of MCK divided by 255*32.
Programming the SCBR field at 0 is forbidden. Triggering a transfer while SCBR is at 0 can lead
to unpredictable results.
At reset, SCBR is 0 and the user has to program it at a valid value before performing the first
transfer.
The divisor can be defined independently for each chip select, as it has to be programmed in the
SCBR field of the Chip Select Registers. This allows the SPI to automatically adapt the baud
rate for each interfaced peripheral without reprogramming.
Figure 28-9
select. Three delays can be programmed to modify the transfer waveforms:
These delays allow the SPI to be adapted to the interfaced peripherals and their speed and bus
release time.
The serial peripherals are selected through the assertion of the NPCS0 to NPCS3 signals. By
default, all the NPCS signals are high before and after each transfer.
The peripheral selection can be performed in two different ways:
• The delay between chip selects, programmable only once for all the chip selects by writing
• The delay before SPCK, independently programmable for each chip select by writing the field
• The delay between consecutive transfers, independently programmable for each chip select
the DLYBCS field in the Mode Register. Allows insertion of a delay between release of one
chip select and before assertion of a new one.
DLYBS. Allows the start of SPCK to be delayed after the chip select has been asserted.
by writing the DLYBCT field. Allows insertion of a delay between two transfers occurring on
the same chip select
DLYBCS
shows a chip select transfer change and consecutive transfers on the same chip
DLYBS
DLYBCT
AT91CAP7E
DLYBCT
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