Rainbow Electronics AT91CAP9S250A - Manual (Page 202)

202
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
22.13 Asynchronous Page Mode
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
Table 22-7 .
With page mode memory devices, the first access to one page (t
pa
) takes longer than the subse-
quent accesses to the page (t
sa
) as shown in Figure 22-34 . When in page mode, the SMC
enables the user to define different read timings for the first access within one page, and next
accesses within the page.
Notes: 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.
22.13.1 Protocol and Timings in Page Mode
Figure 22-34 shows the NRD and NCS timings in page mode access.
Figure 22-34. Page Mode Read Protocol (Address MSB and LSB are defined in Table 22-7 )
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
timings are identical. The pulse length of the first access to the page is defined with the
Table 22-7. Page Address and Data Address within a Page
Page Size Page Address (1) Data Address in the Page (2)
4 bytes A[25:2] A[1:0]
8 bytes A[25:3] A[2:0]
16 bytes A[25:4] A[3:0]
32 bytes A[25:5] A[4:0]
A[MSB]
NCS
MCK
NRD
D[31:0]
NCS_RD_PULSE NRD_PULSE NRD_PULSE
tsa tpa tsa
A[LSB]