External Memory Selection - Philips LPC2119 User Manual

Philips Semiconductors
ARM-based Microcontroller

EXTERNAL MEMORY SELECTION

Based on the description of the EMC operation and external memory in general (appropriate read and write access times t
t respecitely), the following table can be constructed and used for external memory selection. t
WRITE
XCLK cycle (see Figure 10 and Figure 11). f
memory.
Table 10: External memory and system requirements
Access
Max. frequency
cycle
Standard
f <=
max
Read
Standard
f <=
max
Write
External Memory Controller (EMC)
is the maximum pclk frequency achivable in the system with selected external
max
(WST>=0; round up to integer)
2 + WST1
———————
t + 20ns
RAM
1 + WST2
———————
WST2>=
t + 5ns
RAM
WST setting
t + 20ns
RAM
—————— - 2
WST1>=
t
CYC
t - t + 5ns
WRITE CYC
—————————
t
CYC
46
Preliminary User Manual
LPC2119/2129/2292/2294
is the period of a single
CYC
Required memory access time
t <= t *(2+WST1) - 20ns
RAM CYC
t <= t *(1+WST2) - 5ns
WRITE CYC
January 08, 2004
and
AA