7220 Datasheet, PDF (111/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.11 CRT display function
2.11.5 Multi-line display
The M37221M6-XXXSP/FP can ordinarily display 2 lines on the CRT screen by displaying 2 blocks at
different vertical positions. In addition, it can display up to 16 lines by using a CRT interrupt.
A CRT interrupt request occurs at which display of each block has been completed. In other words,
character display of a certain block starts when a scanning line reaches the display position (specified by
vertical position registers) for that block, and an interrupt occurs when the scanning line exceeds the block.
For multi-line display, it is necessary to enable the CRT interrupt (by clearing the interrupt disable flag to
“0” and setting the CRT interrupt enable bit = bit 4 at address 00FE16 to “1”).
In a CRT interrupt processing routine, the character data and vertical position of the block of which display
has been completed (the display as CRT interrupt cause is completed) is then replaced with the character
data (contents of CRT display RAM) and display position (contents of vertical position register) for next
display.
Notes 1: Set the second and later block 1 display start positions of block 1 to be lower than display position
of the last block 2.
2: The CRT interrupt request does not occur at the end of display when the block is not displayed.
In other words, if a block is set to off display with the display control bit of the CRT control
register (at address 00EA16), a CRT interrupt request does not occurs (refer to “Figure 2.11.14”).
Block 1
Block 2
,
Block 1
,
Block 2
Block 1 (on display)
Block 2 (on display)
On display (CRT interrupt request
occurs at the end of block display)
CRT interrupt request
Fig. 2.11.13 Generation timing of CRT interrupt
request
Block 1 (off display)
Block 2 (off display)
Off display (CRT interrupt request does
not occur at the end of block display)
CRT interrupt request
Fig. 2.11.14 Display state of blocks and occurrence
of CRT interrupt request
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7220 Group User’s Manual