AT91SAM9G20_1 Datasheet, PDF (170/832 Pages) ATMEL Corporation – AT91 ARM Thumb Microcontrollers

21.8.3
Write Waveforms
The write protocol is similar to the read protocol. It is depicted in Figure 21-12. The write cycle
starts with the address setting on the memory address bus.
21.8.3.1
NWE Waveforms
The NWE signal is characterized by a setup timing, a pulse width and a hold timing.
1. NWE_SETUP: the NWE setup time is defined as the setup of address and data before
the NWE falling edge;
2. NWE_PULSE: The NWE pulse length is the time between NWE falling edge and NWE
rising edge;
3. NWE_HOLD: The NWE hold time is defined as the hold time of address and data after
the NWE rising edge.
The NWE waveforms apply to all byte-write lines in Byte Write access mode: NWR0 to NWR3.
21.8.3.2
NCS Waveforms
The NCS signal waveforms in write operation are not the same that those applied in read opera-
tions, but are separately defined:
1. NCS_WR_SETUP: the NCS setup time is defined as the setup time of address before
the NCS falling edge.
2. NCS_WR_PULSE: the NCS pulse length is the time between NCS falling edge and
NCS rising edge;
3. NCS_WR_HOLD: the NCS hold time is defined as the hold time of address after the
NCS rising edge.
Figure 21-12. Write Cycle
MCK
A[25:2]
NBS0, NBS1,
NBS2, NBS3,
A0, A1
NWE
NCS
NWE_SETUP
NCS_WR_SETUP
NWE_PULSE
NCS_WR_PULSE
NWE_CYCLE
NWE_HOLD
NCS_WR_HOLD
170 AT91SAM9G20 Preliminary
6384D–ATARM–04-May-09