MC141543

9

MOTOROLA

In order to have better character display within windows, it

is suggested that the designed character font be placed in

the center of the 10 x 16 matrix with equal space on all four

sides. The character $00 is predefined for blank characters,

the character $7F is predefined for full–filled characters, and

the character $7E is a random dot pattern reserved for test-

ing.

In order to avoid submersion of displayed symbols or char-

acters into a background of comparable colors, a feature of

bordering which encircles all four sides, or shadowing which

encircles only the right and bottom sides of an individual dis-

play character, are provided. Figure 7 shows how a character

is jacketed differently. To make sure that a character is bor-

dered or shadowed correctly, at least one blank dot should

be reserved on each side of the character font.

0

14

13

12

11

10

9

8

7

6

5

4

3

2

1

15

Bordering

0

14

13

12

11

10

9

8

7

6

5

4

3

2

1

15

Shadowing

Figure 7. Character Bordering and Shadowing

Frame Format and Timing

Figure 8 illustrates the positions of all display characters

on the screen relative to the leading edge of horizontal and

vertical flyback signals. The shaded area indicates the area

outside “safe viewing area” for the display characters. Notice

that there are two components in the equations stated in Fig-

ure 8 for horizontal and vertical delays: fixed delays from the

leading edge of HFLB and VFLB signals, regardless of the

values of HORD and VERTD (47 dots + phase detection

pulse width) and one H scan line for horizontal and vertical

delays, respectively; and variable delays determined by the

values of HORD and VERTD. Refer to Frame Control Reg-

isters Coln 9 and 10 for the definitions of VERTD and

HORD.

Phase detection pulse width is a function of the external

charge–up resistor, which is the 330 k

Ω resistor in a series

with 2 k

Ω to VCO pin in the Application Diagram. Dot fre-

quency is determined by the equation

H freq x 320 if Bit

X32B is clear, and

H freq x 480 if Bit X32B is set to 1 and Bit

X64 is 0, and

H freq x 640 if both Bit X32B and Bit X64 are

set to 1. For example, dot frequency is 10.24 MHz if H freq is

32 kHz while Bit X32B is 0. If Bit X32B is 1 and Bit X64 is 0,

the dot frequency will be 15.36 MHz (one and a half of the

original one). If Bit X32B is 1 and Bit X64 is also 1, the dot

frequency will be 20.48 MHz (double of the original one).

VFLB

. . . . . .

variable number of H scan lines

vertical delay =

VERTD x 4 + 1 H scan lines

Figure 8. Display Frame Format

When double character width is selected for a row, only the

even–numbered characters will be displayed, as shown in

Row 2. Notice that the total number of horizontal scan lines in

the display frame is variable, depending on the chosen char-

acter height of each row. Care should be taken while config-

uring each row character height so that the last horizontal

scan line in the display frame always comes out before the

leading edge of VFLB of the next frame, to avoid wrapping

display characters of the last few rows in the current frame

into the next frame. The number of display dots in a horizon-

tal scan line is always fixed at 300, regardless of row charac-

ter width and the setting of Bits X32B and X64.