Philips LPC2129 - External Memory Selection; Table 10: External Memory and System Requirements

External Memory Controller (EMC) 62 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2194/2292/2294ARM-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
AA
and
t
WRITE
respecitely), the following table can be constructed and used for external memory selection. t
CYC
is the period of a single
XCLK cycle (see Figure 10 and Figure 11). f
max
is the maximum cclk frequency achievable in the system with selected external
memory.
Table 10: External memory and system requirements
Access
cycle
Max. frequency
WST setting
(WST>=0; round up to integer)
Required memory access time
Standard
Read
2 + WST1
f
max
<= ———————
t
RAM
+ 20ns
t
RAM
+ 20ns
WST1>=
—————— - 2
t
CYC
t
RAM
<= t
CYC
*(2+WST1) - 20ns
Standard
Write
1 + WST2
f
max
<= ———————
t
RAM
+ 5ns
t
WRITE
- t
CYC
+ 5ns
WST2>=
—————————
t
CYC
t
WRITE
<= t
CYC
*(1+WST2) - 5ns