at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 190

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

21.13 Asynchronous Page Mode
21.13.1
Figure 21-35. Page Mode Read Protocol (Address MSB and LSB are defined in
190
AT91SAM9G20 Preliminary
Protocol and Timings in Page Mode
A[MSB]
D[31:0]
A[LSB]
MCK
NRD
NCS
The SMC supports asynchronous burst reads in page mode, providing that the page mode is
enabled in the SMC_MODE register (PMEN field). The page size must be configured in the
SMC_MODE register (PS field) to 4, 8, 16 or 32 bytes.
The page defines a set of consecutive bytes into memory. A 4-byte page (resp. 8-, 16-, 32-byte
page) is always aligned to 4-byte boundaries (resp. 8-, 16-, 32-byte boundaries) of memory. The
MSB of data address defines the address of the page in memory, the LSB of address define the
address of the data in the page as detailed in
With page mode memory devices, the first access to one page (t
quent accesses to the page (t
enables the user to define different read timings for the first access within one page, and next
accesses within the page.
Table 21-7.
Notes:
Figure 21-35
The NRD and NCS signals are held low during all read transfers, whatever the programmed val-
ues of the setup and hold timings in the User Interface may be. Moreover, the NRD and NCS
Page Size
4 bytes
8 bytes
16 bytes
32 bytes
1. A denotes the address bus of the memory device
2. For 16-bit devices, the bit 0 of address is ignored. For 32-bit devices, bits [1:0] are ignored.
NCS_RD_PULSE
shows the NRD and NCS timings in page mode access.
Page Address and Data Address within a Page
tpa
Page Address
A[25:2]
A[25:3]
A[25:4]
A[25:5]
sa
) as shown in
(1)
NRD_PULSE
tsa
Table
Figure
21-7.
Table
21-35. When in page mode, the SMC
Data Address in the Page
A[1:0]
A[2:0]
A[3:0]
A[4:0]
NRD_PULSE
21-7)
pa
tsa
) takes longer than the subse-
6384B–ATARM–15-Dec-08
(2)