are used, one for 2-color characters, the other for 4-color characters. Each of the characters are stored in sequence in the Page

RAM. Special codes are used between lines to show where oneline ends and the next begins, and also to allow blank (or

’skipped’) single scan lines to be added between character rows.

End-Of-Line Code

To signify the end of a line of characters, a special End-of-Line (EOL) code is used in place of a character code. This code, shown

in Table 8 tells the OSD generator that the character and attribute codes which follow must be placed on a new line in the

displayed window. Bits 8–1 are zeros, bit 0 is a one. The attribute that is stored in Page RAM along with this code is not used.

TABLE 8. End-Of-Line Code

ATTRIBUTE CODE

END-OF-LINE CODE

ATT[3:0]

000000001

Skip-Line Code

In order to allow finer control of the vertical spacing of character lines, each displayed line of characters may have up to 15

skipped (i.e., blank) lines between it and the line beneath it. Each skipped line is treated as a single character pixel line, so

multiple scan lines may actually be displayed in order to maintain accurate size relative to the character cell. An internal algorithm

maintains vertical height proportionality (see the section on Constant Character Height Mechanism). To specify the number of

skipped lines, the first character in each new line of characters is interpreted differently than the others in the line. Its data are

interpreted as shown in Table 9, with the attribute bits setting the color of the skipped lines.

TABLE 9. Skipped-Line Code

ATTRIBUTE CODE

NUMBER OF SKIPPED LINES

ATT[3:0]

XXXXX

SL[3:0]

Bits 8–4 are reserved and should be set to zero. Bits 3–0 determine how many blank pixel lines will be inserted between the

present line of display characters and the next. A range of 0–15 may be selected. Bits 12–9 determine which attribute the pixels

in the skipped lines will have, which is always called from the two-color attribute table. The pixels will have the background color

(Color 0) of the selected attribute table entry.

Note that the pixels in the first line immediately below the character may be overwritten by the pixel override system that creates

the button box. (Refer to the Button Box Formation Section for more information).

After the first line, each new line always starts with an SL code, even if the number of skipped lines to follow is zero. This means

an SL code must always follow an EOL code. An EOL code may follow an SL code if several ’transparent’ lines are required

between sections of the window. See example 3 below for a case where skipped lines of zero characters are displayed, resulting

in one window being displayed in two segments.

End-Of-Screen Code

To signify the end of the window, a special End-Of-Screen (EOS) code is used in place of a End-Of-Line (EOL) code. There must

be at least one EOS code in the Page RAM to avoid unpredictable behavior. This can be accomplished by clearing the RAM by

writinga0tobit3ofthe FRMCTRL1 Register, 0x8400, immediately after power up.

TABLE 10. End-Of-Screen Code

ATTRIBUTE CODE

END-OF-SCREEN CODE

ATT[3:0]

000000000

Bits 8–0 are all zeros. Bits 12–9 will have the previously entered AC but this is not used and so these bits are “don’t cares”.

OSD CONTROL REGISTERS

These registers, shown in Table 11, control the size, position, and enhanced features of up to two independent OSD windows. Any

bits marked as “X” are reserved and should be written to with zeros and should be ignored when the register is read. Additional

register detail is provided in the Control Register Definitions Section, later in this document.

TABLE 11. OSD Control Register Detail

Register

Address

Default

D7

D6

D5

D4

D3

D2

D1

D0

FRMCTRL1

0x8400

0x98

HTD

X

FEN

TD

CDPR

D2E

D1E

OSE

FRMCTRL2

0x8401

0x80

PIXELS_PER_LINE[2:0]

BLINK_PERIOD[4:0]

CHARFONTACC

0x8402

0x00

XXXXXX

ATTR

FONT4

VBLANKDUR

0x8403

0x10

X

VBLANK_DURATION[6:0]

CHARHTCTRL

0x8404

0x51

CHAR_HEIGHT[7:0]

BBHLCTRLB0

0x8405

0xFF

B[1:0]

G[2:0]

R[2:0]

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