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FUNCTIONAL DESCRIPTION
2.11 CRT display function
2.11.1 Display position
The display positions of characters are specified in units called a "block". There are 2 blocks, block 1 and
block 2. Up to 24 characters can be displayed in 1 block (refer to "2.11.3 Memory for display").
The display position of each block in both horizontal and vertical directions can be set by software.
The horizontal direction is common to all blocks, and is selected from 64-step display positions in units of
4 T
(T
= oscillation cycle for display).
C
C
The display position in the vertical direction is selected from 128-step display positions for each block in
units of 4 scanning lines. The display position in the vertical direction is determined by counting the
horizontal sync signal (H
At this time, it starts to count the rising edge (falling edge ) of H
of rising edge (falling edge ) of V
needs enough time (2 machine cycles or more) for avoiding jitter.
:The polarity of H
SYNC
When clearing corresponding bits to "0," positive polarity is selected, when setting to "1," negative
polarity is selected. Refer to "2.11.7 CRT output pin control" for detail.
V
signal input
SYNC
V
control signal
SYNC
in microcomputer
Period of counting
H
signal
SYNC
H
signal input
SYNC
8 machine cycles or more
(See note 4)
Fig. 2.11.4 Count method of synchronous signal
2-74
).
SYNC
signal. So interval from rising edge (falling edge ) of H
SYNC
and V
signals can select by the CRT port control register (address 00EC
SYNC
0.125 µ s to 0.25 µ s (See note 2)
(See note 3)
↑
↑
Not count
1
When bits 0 and 1 of the CRT port control register (address 00EC
are set to "1" (negative polarity)
Note 1: The vertical position is determined by counting falling
edge of H
signal in the microcomputer.
2: At f(X
) = 8 MHz
IN
3: Do not generate falling edge of H
of V
SYNC
4: Pulse width of V
cycles or more.
7220 Group User's Manual
signal from after about 1 machine cycle
SYNC
8 machine cycles or more (See note 4)
↑
↑
2
3
signal after rising edge of V
SYNC
control signal in microcomputer to avoid jitter.
and of H
SYNC
SYNC
↑
↑
4
5
control
SYNC
signal near rising edge
SYNC
signals needs 8 machine
signal
SYNC
).
16
)
16
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