TMPR3916 datasheet(88/225 Pages) TOSHIBA

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Chapter 3 Graphics Display Controller (GDC)

Preliminary

3-9

3.2

Scrolling

There are two different ways of scrolling when using the TMPR3916’s graphics display controller:

Smooth scrolling and some kind of register scrolling.

Smooth scrolling is done by changing the start address of graphics data in memory (SARx). The layers in

TMPR3916 have different resolutions in colour depth. That is why the number of dots per word changes

from layer to layer. Therefore the address of the next dot for display differs. This implies different handling

of smooth scrolling in the different kinds of layers.

The easiest implementation can be reached using layers C and D. It is also the type of implementation this

document starts with. Following is the description for layers A and B.

vertical display start and end. As layers A, B, C and E have common settings for display size and are

normally fixed to the display’s maximum settings, this scrolling type only applies to layer D. The related

registers are HDSERD, VDSRD and VDERD.

The algorithms following are based on C syntax for documentation. They also imply just one step at a time

in one direction. For moving in several directions at the same step the related algorithm has to be executed

for each direction. For example, if scrolling to the left and up is wanted, two runs of the algorithm are needed

– one for “LEFT”, one for “UP”.

It is assumed that only four directions have been defined: LEFT, RIGHT, UP and DOWN. This is why the

“UP” decision automatically branches into “DOWN” case if false.

3.2.1

Smooth Scrolling

3.2.1.1

Scrolling Layers C and D

For smooth scrolling three bits are reserved in start address register (SARx). As layer C and D

both consist of data with eight dots per word and this is the maximum amount of differing

addresses that can be generated using three bits for coding, no problem occurs for these layers:

Just add (subtract) to (from) SARx the amount of dots you want to use as offset for smooth

scrolling to the left (right) or respectively up (down). The related algorithm is shown in the

following diagram:

newSARx = SARD

newSARx = SARC

MWRx = MWRC >> 15

MWRx = MWRD >> 15

LEFT

True

False

RIGHT

True

False

True

False

newSARx += offset

newSARx -= offset

newSARx += MWR * offset * 4

newSARx -= MWR * offset * 4

SARD = newSARx

SARC = newSARx

LAYER_C

True

False

LAYER_C

True

False

Example:

For scrolling a picture located at 0x50010024 (SARx: 0xA0020048) to the left by one dot

simply add 0x01 to the latter value: 0xA0020049 is the correct start address register value for the

next picture (physical: 0x50010024). Note that the least significant bits in this start adress register

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