7220 Datasheet, PDF (178/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPLICATION
5.1 Example of multi-line display
(3) CRT interrupt processing routine
The CRT interrupt processing routine executes the display character data setup routine for each line,
in order to perform multi-line display. The line to be displayed is determined by the line counter value.
ICON1, ICON2: Interrupt control registers 1, 2
CS : Character size register
HR : Horizontal position register
Line counter : Counter RAM for line counting
CV1,CV2 : Vertical position registers 1, 2
CRT_ICON1, CRT_ICON2 : Back up RAM for interrupt control
CRT interrupt processing routine
registers 1, 2 during CRT interrupt
A : Accumulator
X : Index register X
T
D
CRT_ICON1
←“0”
←“0”
←ICON1
Y : Index register Y
T : X modified operation mode flag
D : Decimal operation mode flag
CRT_ICON2
←ICON2
ICON1 (address 00FE 16) ←“001000012” _{← Enable Timer 1 interrupt and}
ICON2 (address 00FF 16) ←“000000002” _{VSYNC interrupt}
I
←“0”
Push registers X, Y, A
← Specify jump destination by
Line counter value
Line counter = 0
Block 1 display RAM ←
Display character of block 1 (the 1st line)
Character color of block 1 (the 1st line)
CV1 ← Vertical display start position
of the 1st line (block 1)
Set CS, HR
=1
Block 2 display RAM ←
Display character of block 2 (the 2nd line)
Character color of block 2 (the 2nd line)
CV2 ← Vertical display start position
of the 2nd line (block 2)
Set CS, HR
= 11
Block 2 display RAM ←
Display character of block 2 (the 12th line)
Character color of block 2 (the 12th line)
CV2 ← Vertical display start position
of the 12th line (block 2)
Set CS, HR
Line counter +1
≠12
Line counter =12
=12
Line counter ← “0”
Save the value of Line counter
in internal RAM
Pop registers X, Y, A
I
ICON1
ICON2
←“1”
←CRT_ICON1
←CRT_ICON2
←Disable all interrupts
←Pop ICON 1 and 2 contents during
CRT interrupt (Refer to “5.1.7 (2)”)
RETURN
Note: The multiple interrupt priority of
this system is as below.
Timer 1 > VSYNC > CRT
Fig. 5.1.5 Flowchart of CRT interrupt processing routine
7220 Group User’s Manual
5-5