
5-2
External Memory Interface
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
and the number of macroblock rows.
Equation 5.1 may be used to cal-
culate the amount of memory needed in regular memory mode.
Equation 5.1
In
Equation 5.1, the frame store memory is equal to three times the num-
ber of pixels multiplied by the number of lines multiplied by 1.5. For
example, if the picture size is 720 pixels by 480 lines, then Frame Store
Memory is equal to 3 x 720 x 480 x 1.5, or 1,555,200 bytes. For bit-
streams with no B-frames, only two frame stores are needed. See
Sec-An 18-bit addressing range in the L64005 memory space allows access
to up to 256K 64-bit words.
5.3
Memory
Interface
The Memory interface is optimized for use with four 4-Mbit DRAMs or
with one 16-Mbit synchronous DRAM.
5.3.1
Regular DRAM
Mode
The typical set of 4-Mbit DRAMs are 70-ns devices operating in fast page
mode at the nominal device clock of 27 MHz. The L64005 limits the
allowable page length to 512 words (4096 bytes), regardless of the mem-
ory type used. The L64005 interface provides a single 9-bit row/column
multiplexed address bus for accessing the DRAMs;
Table 5.1 shows the
mapping of the physical address bus to the BA[8:0] pins. Output drivers
drive 50-pF loads at the rated speed.
Figure 5.1 further illustrates the I/O
interface between the L64005 and the 4-Mbit DRAMs.
Frame Store Memory
3 Frame Stores
Pixels Line
Lines
1.5 bytes
×
×
=