LM1236 Address Map
(Continued)
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
ATT[3:0]
END-OF-LINE CODE
0
0
0
0
0
0
0
0
1
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
ATT[3:0]
NUMBER OF SKIPPED LINES
X
X
X
X
X
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
writing a 0 to bit 3 of the FRMCTRL1 Register, 0x8400, immediately after power up.
TABLE 10. End-Of-Screen Code
ATTRIBUTE CODE
ATT[3:0]
END-OF-SCREEN CODE
0
0
0
0
0
0
0
0
0
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
FRMCTRL1
FRMCTRL2
CHARFONTACC
VBLANKDUR
CHARHTCTRL
BBHLCTRLB0
Address
0x8400
0x8401
0x8402
0x8403
0x8404
0x8405
Default
0x98
0x80
0x00
0x10
0x51
0xFF
D7
HTD
PIXELS_PER_LINE[2:0]
X
X
X
D6
X
D5
FEN
D4
TD
D3
D2
D2E
D1
D1E
D0
OSE
CDPR
BLINK_PERIOD[4:0]
X
X
X
X
ATTR
FONT4
VBLANK_DURATION[6:0]
CHAR_HEIGHT[7:0]
G[2:0]
B[1:0]
R[2:0]
L
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