UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
27 of 362
NXP Semiconductors
UM10208
Chapter 4: LPC2800 Cache
2. CPU clock gating off, fractional divider set to 1/7.
In this case, the AHB fractional divider has been set to generate a bus clock once
every 7 base clock cycles.
3. CPU clock gating enabled, fractional divider set to 1/7.
In this case, CPU clock gating has been enabled. The CPU clock enable signal is
generated by the cache when the CPU must wait because either the cache is reading
or writing data on the AHB bus, or the cache is jumping in between cache lines,
adding a single wait state.
Fig 6.
Cache and CPU clock timing
CPU clock
AHB0 clock
Internal cache clock
Internal CPU clock
CPU clock enable
Case 1: CPU clock gating off, fractional divider not used.
CPU clock
AHB0 Clock
Internal cache clock
Internal CPU clock
CPU clock enable
Case 2: CPU clock gating off, fractional divider set to 1/7.
CPU clock
AHB0 Clock
Internal cache clock
Internal CPU clock
CPU clock enable
Case 3: CPU clock gating enabled, fractional divider set to 1/7.