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LCD Controller
4-20
MC68328 DRAGONBALL PROCESSOR USER’S MANUAL
MOTOROLA
4.8 BANDWIDTH CALCULATION AND SAVING
Because LCD screen refresh is a periodic task, the load LCDC puts on the host data bus
becomes an important consideration to the high-performance handheld system designer.
4.8.1 Bus Overhead Considerations
The following example illustrates the issues involved in the estimation of bandwidth
overhead to the data bus.
Consider a typical case scenario:
Screen size: 320 x 240 pixels
Bits per pixel: 2 bits / pixel
Screen refresh rate: 60 Hz
System clock = 16.67 MHz
Host bus size: 16 bit
DMA access cycle: 2 cycles per 16-bit word
The period,
T
l
,, that LCDC must update one line of the screen is,
(EQ 1)
At the same period, the line buffer must be filled. The duration,
T
DMA
, which the DMA cycle
will take up the bus is,
(EQ 2)
Thus, the percentage of host bus time taken up by the LCDC DMA is
P
DMA
,
(EQ
3)
T
l
1
60Hz
-------------
1
240lines
--------------------
×
=
69.4
µ
s
=
T
DMA
320pixels
2bitperpixel
×
2clock
×
16.67MHz
16bitbus
×
--------------------------------------------------------------------------------------
=
4.8
µ
s
=
P
DMA
4.8`
µ
s
69.4`
µ
s
-------------------
=
6.92
=
%
Содержание DragonBall MC68328
Страница 5: ...vi MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 25: ...Overview 1 14 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 45: ...System Integration Module 2 20 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 103: ...Parallel Ports 7 16 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 117: ...UART 8 14 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 127: ...SPI Master 10 6 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Страница 137: ...Electrical Characteristics PRELIMINARY MOTOROLA MC68328 DRAGONBALL PROCESSOR USER S MANUAL 13 4 ...