at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 177
at91sam9g20-cu
Manufacturer Part Number
at91sam9g20-cu
Description
At91 Arm Thumb Microcontrollers
Manufacturer
ATMEL Corporation
Datasheet
1.AT91SAM9G20-CU.pdf
(814 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
AT91SAM9G20-CU
Manufacturer:
Atmel
Quantity:
5
Company:
Part Number:
AT91SAM9G20-CU
Manufacturer:
ATMEL
Quantity:
188
- Current page: 177 of 814
- Download datasheet (13Mb)
21.10 Data Float Wait States
21.10.1
6384B–ATARM–15-Dec-08
READ_MODE
Some memory devices are slow to release the external bus. For such devices, it is necessary to
add wait states (data float wait states) after a read access:
The Data Float Output Time (t
TDF_CYCLES field of the SMC_MODE register for the corresponding chip select. The value of
TDF_CYCLES indicates the number of data float wait cycles (between 0 and 15) before the
external device releases the bus, and represents the time allowed for the data output to go to
high impedance after the memory is disabled.
Data float wait states do not delay internal memory accesses. Hence, a single access to an
external memory with long t
memory.
The data float wait states management depends on the READ_MODE and the TDF_MODE
fields of the SMC_MODE register for the corresponding chip select.
Setting the READ_MODE to 1 indicates to the SMC that the NRD signal is responsible for turn-
ing off the tri-state buffers of the external memory device. The Data Float Period then begins
after the rising edge of the NRD signal and lasts TDF_CYCLES MCK cycles.
When the read operation is controlled by the NCS signal (READ_MODE = 0), the TDF field gives
the number of MCK cycles during which the data bus remains busy after the rising edge of NCS.
Figure 21-21
assuming a data float period of 2 cycles (TDF_CYCLES = 2).
ation when controlled by NCS (READ_MODE = 0) and the TDF_CYCLES parameter equals 3.
• before starting a read access to a different external memory
• before starting a write access to the same device or to a different external one.
illustrates the Data Float Period in NRD-controlled mode (READ_MODE =1),
DF
will not slow down the execution of a program from internal
DF
) for each external memory device is programmed in the
AT91SAM9G20 Preliminary
Figure 21-22
shows the read oper-
177
Related parts for at91sam9g20-cu
Image
Part Number
Description
Manufacturer
Datasheet
Request
R
Part Number:
Description:
INTERVAL AND WIPE/WASH WIPER CONTROL IC WITH DELAY
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
Low-Voltage Voice-Switched IC for Hands-Free Operation
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
MONOLITHIC INTEGRATED FEATUREPHONE CIRCUIT
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
AM-FM Receiver IC U4255BM-M
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
Monolithic Integrated Feature Phone Circuit
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
Multistandard Video-IF and Quasi Parallel Sound Processing
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
High-performance EE PLD
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
8-bit Flash Microcontroller
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
2-Wire Serial EEPROM
Manufacturer:
ATMEL Corporation
Datasheet:
Part Number:
Description:
U6046BREAR WINDOW HEATING TIMER / LONG-TERM TIMER
Manufacturer:
ATMEL Corporation
Datasheet: