LM1247 National Semiconductor, LM1247 Datasheet - Page 33

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

Control Register Definitions
Frame Control Register 2:
Character Font Access Register:
Vertical Blank Duration Register:
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bits 7–5
Bits 4–0
Bits 7–5
Bit 0
Bit 1
Bits 7–2
On-Screen Display Enable. The On-Screen Display will be disabled when this bit is a zero. When this bit is a
one the On-Screen Display will be enabled. This controls both Window 1 and Window 2.
Display Window 1 Enable. When this bit and Bit 0 of this register are both ones, Display Window 1 is enabled.
If either bit is a zero, then Display Window 1 will be disabled.
Display Window 2 Enable. When this bit and Bit 0 of this register are both ones, Display Window 2 is enabled.
If either bit is a zero, then Display Window 2 will be disabled.
Clear Display Page RAM. Writing a one to this bit will result in setting all of the Display Page RAM values to
zero. This bit is automatically cleared after the operation is complete.
Transparent Disable. When this bit is a zero, a palette color of black (i.e., color palette look-up table value of
0x00) in the first 8 palette look-up table address locations (i.e., ATT0–ATT7) will be interpreted as transparent.
When this bit is a one, the color will be interpreted as black.
Reserved (Should be set to zero)
Blinking Period. These five bits set the blinking period of the blinking feature, which is determined by
mulitiplying the value of these bits by 8, and then multiplying the result by the vertical field rate.
Pixels per Line. These three bits determine the number of pixels per line of OSD characters. See Table 21
which gives the maximum horizontal scan rate. Also see Table 3 since the maximum recommended scan rate
is also a function of the PLLFREQRNG register, 0x843E[1:0].
This is the Color Bit Plane Selector. This bit must be set to 0 to read or write a two-color attribute from the
range 0x0000 to 0x2FFF. When reading or writing four-color attributes from the range 0x3000 to 0x3FFF, this
bit is set to 0 for the least significant plane and to 1 for the most significant plane. It is also required to set this
bit to read the individual bit planes of the four color character fonts in 0x3000 to 0x3FFF and 0x7000 to
0x7FFF.
This is the Character/Attribute Selector. This applies to reads from the Display Page RAM (address range
0x8000–0x81FF). When a 0, the character code is returned and when a 1, the attribute code is returned.
Reserved. These should be set to zero.
Bits 7–5
0x0
0x1
0x2
0x3
0x4
0x5
0x6
0x7
Res’d
X
X
Pixels per Line
PL[2:0]
X
TABLE 21. OSD Pixels per Line
X
Reserved
(Continued)
CHARFONTACC (0x8402)
VBLANKDUR (0x8403)
FRMCTRL1 (0x8401)
Vertical Blanking Duration
512 pixels per line
576 pixels per line
640 pixels per line
704 pixels per line
768 pixels per line
832 pixels per line
896 pixels per line
960 pixels per line
Description
X
33
VB[6:0]
X
Blink Period
BP[4:0]
X
Select
C/A
Max Horizontal Frequency (kHz)
Plane
Bit
125
106
100
119
112
93
87
81
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