7220 datasheet(181/303 Pages) RENESAS

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APPLICATION

5.1 Example of multi-line display

7220 Group User’s Manual

5-8

5.1.6 Processing time

When setting display data by a CRT interrupt, the processing time is limited.

As shown in Figure 5.1.7, a CRT interrupt occurs at the end of the first line (block 1) display and setting

for the 3rd line display is started. This setting must be completed before a scanning line reaches to the

3rd line display position. If the setting is not completed, display characters flicker or rewriting is looked.

And also, for multi-line display of 12 lines, be sure that CRT interrupts occur 12 times from a VSYNC to the

next VSYNC. If CRT interrupts do not occur as many times as the number of display lines, the following

causes can be assumed.

• Display position overlaps.

• CRT interrupt processing time is too long, resulting in no display of that line (2 lines after the line being

displayed).

For example, a CRT interrupt occurs at the end of the second line display in Figure 5.1.7. Within this

interrupt processing, setting for the 4th line display is completed. However, if a scanning line is over the

display position of the 4th line (that is, A in Figure 5.1.7) during this setting, one CRT interrupt request is

deleted (or does not occur). Therefore, the line counter value is disordered and multi-line display is not

displayed correctly. In such cases, due to whatever causes, correct the value with processing C of VSYNC

interrupt processing (refer to “Figure 5.1.4”). When the CRT interrupt software processing overtime causes

this state, change the display positions or shorten the CRT interrupt software processing time.

7220 Datasheet(PDF) 181 Page - Renesas Technology Corp