TMP92CF30
2009-06-15
92CF30-170
3.8.5
Notes
(1)
Timing for the
CS
and
RD
signals
If the load capacitance of the
RD
(Read) signal line is greater than that of the
CS
(Chip
Select) signal line, the deassertion timing of the read signal is delayed, which may lead to
an unintentional extension of a read cycle. Such an unintended read cycle extension,
which is indicated as (a) in Figure 3.8.6, may cause a problem.
Figure 3.8.6 Read Cycle of When the Read Signal is Delayed
Example: When using an externally connected NOR flash whose commands are compatible with the standard
JEDEC commands, the toggle bit may not be read correctly. If the rising edge of the read signal in the cycle
immediately preceding the NOR flash access cycle does not occur in time, a read cycle may be extended
unintentilnally as indicated as (b) in Figure 3.8.7.
Figure 3.8.7 NOR Flash Toggle Bit Read Cycle
When the toggle bit is inverted due to this unexpected read cycle extension, the CPU
cannot read the toggle bit properly and it always reads the same value from the toggle bit.
To avoid this situation, it is recommended to perform data polling or to use the timing
adjustment function for the rising edge of the
RD
signal (RDTMGCRn
<BnTCRH1:BnTCRH0>).
RD
A23 to A0
SDCLK
(20 MHz)
CSm
CSn
(a)
A23 to A0
SDCLK
(20 MHz)
NOR flash
chip select
RD
(b)
Toggle bit
Memory access
Toggle bit RD cycle
Summary of Contents for TLCS-900/H1 Series
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