Datasheet
2017 Microchip Technology Inc. DS60001516A-page 179
SAM9G20
The SMC does not check the coherency of timings. It will always apply the NCS_RD_PULSE timings as page access timing (t
pa
) and the
NRD_PULSE for accesses to the page (t
sa
), even if the programmed value for t
pa
is shorter than the programmed value for t
sa
.
20.13.2 Byte Access Type in Page Mode
The Byte Access Type configuration remains active in page mode. For 16-bit or 32-bit page mode devices that require byte selection sig-
nals, configure the BAT field of the SMC_REGISTER to 0 (byte select access type).
20.13.3 Page Mode Restriction
The page mode is not compatible with the use of the NWAIT signal. Using the page mode and the NWAIT signal may lead to unpredictable
behavior.
20.13.4 Sequential and Non-sequential Accesses
If the chip select and the MSB of addresses as defined in Table 20-6 are identical, then the current access lies in the same page as the
previous one, and no page break occurs.
Using this information, all data within the same page, sequential or not sequential, are accessed with a minimum access time (t
sa
).
Figure 20-35 illustrates access to an 8-bit memory device in page mode, with 8-byte pages. Access to D1 causes a page access with a
long access time (t
pa
). Accesses to D3 and D7, though they are not sequential accesses, only require a short access time (t
sa
).
If the MSB of addresses are different, the SMC performs the access of a new page. In the same way, if the chip select is different from the
previous access, a page break occurs. If two sequential accesses are made to the page mode memory, but separated by an other internal
or external peripheral access, a page break occurs on the second access because the chip select of the device was deasserted between
both accesses.
Table 20-7: Programming of Read Timings in Page Mode
Parameter Value Definition
READ_MODE ‘x’ No impact
NCS_RD_SETUP ‘x’ No impact
NCS_RD_PULSE t
pa
Access time of first access to the page
NRD_SETUP ‘x’ No impact
NRD_PULSE t
sa
Access time of subsequent accesses in the page
NRD_CYCLE ‘x’ No impact