lh79520 NXP Semiconductors, lh79520 Datasheet - Page 31

• Manufacturer Part Number: lh79520
• Description: Lh79520 System-on-chip
• Manufacturer: NXP Semiconductors

System-on-Chip
Static Memory Controller Waveforms
nWAIT INPUT
nWAIT input that can be used by an external device to
extend the wait time during a memory access. The
SMC samples nWAIT at the beginning of at the begin-
ning of each system clock cycle. The system clock
cycle in which the nCSx signal is asserted counts as
the first wait state. See Figure 11.
clock cycles after it has been asserted. To assure that
the current access (read or write) will be extended by
nWAIT, at least two wait states must be programmed
for this bank of memory. If N wait states are pro-
grammed, then the Static Memory Controller (SMC)
holds this state for N system clocks, or until the SMC
detects that nWAIT is inactive, whichever occurs last.
As the number of wait states programmed increases,
the amount of delay before nWAIT must be asserted
also increases. If only 2 wait states are programmed,
Preliminary data sheet
The Static Memory Controller (SMC) supports an
The SMC recognizes that nWAIT is active within 2
Rev. 01 — 16 July 2007
NXP Semiconductors
then nWAIT must be asserted in the clock cycle imme-
diately following the clock cycle during which the nCSx
signal is asserted. Once the SMC detects that the
external device has deactivated nWAIT, the SMC will
complete its access in 3 system clock cycles.
ing nCSx and asserting nWAIT is:
READ AND WRITE WAVEFORMS
External Static Memory Write. Figure 13 shows the
waveform and timing for an External Static Memory
Read, with one Wait State. Figure 14 shows the wave-
form and timing for an External Static Memory Read,
with two Wait States.
measurements are made from the Address Valid point
and HCLK is an internal signal, shown for reference only.
The formula for the allowable delay between assert-
tASSERT = (system clock period) × (Wait States - 1)
(where Wait States is from 2 to 31.)
Figure 12 shows the waveform and timing for an
The signal tIDD is shown without a setup time, as
LH79520
31